Low viscosity precursor compositions and methods for the deposition of conductive electronic features

ABSTRACT

A precursor composition for the deposition and formation of an electrical feature such as a conductive feature. The precursor composition advantageously has a low viscosity enabling deposition using direct-write tools. The precursor composition also has a low conversion temperature, enabling the deposition and conversion to an electrical feature on low temperature substrates. A particularly preferred precursor composition includes silver metal for the formation of highly conductive silver features.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 10/265,351, filed Oct. 4, 2002, which claims thebenefit of U.S. Provisional Application No. 60/327,620 filed Oct. 5,2001. Each of the foregoing referenced patent applications isincorporated by reference herein as if set forth below in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to precursor compositions that are usefulfor the deposition of conductive electronic features. The precursorcompositions can advantageously have a low conversion temperature toenable low-temperature treatment of the precursors to form conductiveelectronic features on a variety of substrates. The precursorcompositions can also have a low viscosity to enable the deposition ofthe compositions using direct-write tools, such as ink-jet devices.

2. Description of Related Art

The electronics, display and energy industries rely on the formation ofcoatings and patterns of conductive materials to form circuits onorganic and inorganic substrates. The primary methods for generatingthese patterns are screen printing for features larger than about 100 μmand thin film and etching methods for features smaller than about 100μm. Other subtractive methods to attain fine feature sizes include theuse of photo-patternable pastes and laser trimming.

One consideration with respect to patterning of conductors is cost.Non-vacuum, additive methods generally entail lower costs than vacuumand subtractive approaches. Some of these printing approaches utilizehigh viscosity flowable liquids. Screen-printing, for example, usesflowable mediums with viscosities of thousands of centipoise. At theother extreme, low viscosity compositions can be deposited by methodssuch as ink-jet printing. However, this latter family of low viscositycompositions is not as well developed as the high viscositycompositions.

Ink-jet printing of conductors has been explored, but the approaches todate have been inadequate for producing well-defined features with goodelectrical properties. For example, ink-jet printable conductorcompositions have been described by R. W. Vest (Metallo-OrganicMaterials for Improved Thick Film Reliability, Nov. 1, 1980, FinalReport, Contract #N00163-79-C-0352, National Avionic Center). Thecompositions disclosed by Vest included a precursor and a solvent forthe precursor. These compositions were not designed for processing atlow temperatures, and as a result the processing temperatures wererelatively high, such as greater than 250° C.

U.S. Pat. Nos. 5,882,722 and 6,036,889 by Kydd disclose conductorprecursor compositions that contain metallic particles, a precursor anda vehicle and are capable of forming conductors at low temperatures onorganic substrates. However, the formulations have a relatively highviscosity and are not useful for alternative deposition methods such asink-jet printing.

Attempts have also been made to produce metal-containing compositions atlow temperatures by using a composition containing a polymer and aprecursor to a metal. See, for example, U.S. Pat. No. 6,019,926 bySouthward et al. However, the deposits were chosen for opticalproperties and were either not conductive or were poorly conductive.

U.S. Pat. Nos. 5,846,615 and 5,894,038, both by Sharma et al., discloseprecursors to Au and Pd that have low reaction temperatures therebyconceptually enabling processing at low temperatures to form metals. Itis disclosed that a variety of methods can be used to apply theprecursors, including ink-jet printing and screen printing. However, theprinting of these compositions is not disclosed in detail.

U.S. Pat. No. 5,332,646 by Wright et al. discloses a method of makingcolloidal palladium and/or platinum metal dispersions by reducing apalladium and/or platinum metal of a metallo-organic palladium and/orplatinum metal salt which lacks halide functionality. However,formulations for depositing electronic features are not disclosed.

U.S. Pat. No. 5,176,744 by Muller discloses the use of Cu-formateprecursor compositions for the direct laser writing of copper metal. Thecompositions include a crystallization inhibitor to preventcrystallization of copper formate during drying.

U.S. Pat. No. 5,997,044 by Behm et al. discloses a document, such as alottery ticket, having simple circuitry deposited thereon. The circuitrycan be formed from inks containing conductive carbon and other additivesas well as metallic particles. It is disclosed that the inks can bedeposited by methods such as gravure printing.

U.S. Pat. No. 6,238,734 by Senzaki et al. is directed to compositionsfor the chemical vapor deposition of mixed metal or metal compoundlayers. The method uses a solventless common ligand mixture of metals ina liquid state for deposition by direct liquid injection.

There exists a need for low viscosity precursor compositions for thefabrication of conductive features for use in electronics, displays, andother applications. Further, there is a need for precursor compositionsthat have low processing temperatures to allow deposition onto organicsubstrates and subsequent heat treatment. It would also be advantageousif the compositions could be deposited with a fine feature size, such asnot greater than 100 Am, while still providing electronic features withadequate electrical and mechanical properties.

The ideal low viscosity precursor composition and its associateddeposition technique for the fabrication of electronic features such asa conductor would combine a number of attributes. The conductive featurewould have high conductivity, preferably close to that of a dense, puremetal. The processing temperature would be low enough to allow formationof conductors on a variety of organic substrates. The depositiontechnique would allow deposition onto surfaces that are non-planar(e.g., not flat). The conductive feature would have high resistance toelectromigration, solder leaching and oxidation. The conductor wouldalso have good adhesion to the substrate.

Further, there is a need for electronic circuit elements and completeelectronic circuits fabricated on inexpensive, thin and/or flexiblesubstrates, such as paper, using high volume printing techniques such asreel-to-reel printing. Recent developments in organic thin filmtransistor (TFT) technology and organic light emitting device (OLED)technology have accelerated the need for complimentary circuit elementsthat can be written directly onto low cost substrates. Such elementsinclude conductive interconnects, electrodes, conductive contacts andvia fills.

DESCRIPTION OF THE INVENTION

The present invention is directed to low viscosity precursorcompositions that can be deposited onto a substrate using, for example,direct-write methods such as ink-jet deposition. The precursorcompositions preferably have a low decomposition temperature, therebyenabling the formation of electronic features on a variety ofsubstrates, including organic substrates. The precursor compositions caninclude various combinations of molecular metal precursors, solvents,micron-sized particles, nanoparticles, vehicles, reducing agents andother additives. The precursor compositions can advantageously includeone or more conversion reaction inducing agents adapted to reduce theconversion temperature of the precursor composition. The precursorcompositions can be deposited onto a substrate and reacted to formhighly conductive electronic features having good electrical, andmechanical properties.

The precursor compositions according to the present invention can beformulated to have a wide range of properties and a wide range ofrelative cost. For example, in high volume applications that do notrequire well-controlled properties, inexpensive precursor compositionscan be deposited on cellulose-based materials, such as paper, to formsimple disposable circuits.

On the other hand, the precursor compositions of the present inventioncan be utilized to form complex, high precision circuitry having goodelectrical properties. For example, the compositions and methods of thepresent invention can be utilized to form conductive features on asubstrate, wherein the features have a feature size (i.e., average widthof the smallest dimension) of not greater than about 200 micrometers(Am), more preferably not greater than about 100 μm, even morepreferably not greater than about 75 μm, even more preferably notgreater than about 50 μm and most preferably not greater than about 25μm.

The conductive electronic features formed according to the presentinvention can have good electrical properties. For example, theconductive features according to the present invention can have aresistivity that is not greater than 20 times the resistivity of thebulk conductor, such as not greater than 10 times the resistivity of thebulk conductor, preferably not greater than 6 times the resistivity ofthe bulk conductor, more preferably not greater than 4 times theresistivity of the bulk conductor and even more preferably not greaterthan 2 times the resistivity of the bulk conductor.

The method for forming the electronic features according to the presentinvention can also use relatively low processing temperatures. In oneembodiment, the conversion temperature is not greater than about 250°C., such as not greater than about 225° C., more preferably is notgreater than about 200° C. and even more preferably is not greater thanabout 185° C. In certain embodiments, the conversion temperature can benot greater than about 150° C., such as not greater than about 125° C.and even not greater than about 100° C.

Definitions

As used herein, the term low viscosity precursor composition refers to aflowable composition that has a viscosity of not greater than about 1000centipoise. According to one embodiment, the low viscosity precursorcomposition has a viscosity of not greater than about 500 centipoise,more preferably not greater than about 100 centipoise and even morepreferably not greater than about 50 centipoise. As used herein, theviscosity is measured at a shear rate of about 132 Hz and under therelevant deposition conditions, particularly temperature. For example,some precursor compositions may be heated prior to deposition to reducethe viscosity.

As used herein, the term molecular metal precursor refers to a molecularcompound that includes a metal atom. Examples include organometallics(molecules with carbon-metal bonds), metal organics (moleculescontaining organic ligands with metal bonds to other types of elementssuch as oxygen, nitrogen or sulfur) and inorganic compounds such asmetal nitrates, metal halides and other metal salts.

The low viscosity precursor compositions in accordance with the presentinvention can also include particulates of a metal other materialphases. The particulates can fall in two size ranges referred to hereinas nanoparticles and micron-size particles. Nanoparticles have anaverage size of not greater than about 100 nanometers. Micron-sizeparticles have an average particle size of greater than about 0.1 μm.Nanoparticles and micron-size particles are collectively referred toherein as particles or powders.

In addition, the low viscosity precursor compositions can include asolvent for the molecular metal precursor. A solvent is a chemical thatis capable of dissolving at least a portion of the molecular metalprecursor. The low viscosity precursor composition can also include avehicle. As used herein, a vehicle is a flowable medium that facilitatesdeposition of the precursor composition, such as by imparting sufficientflow properties or supporting dispersed particles. As will beappreciated from the following discussion, the same chemical compoundcan have multiple functions in the precursor composition, such as onethat is both a solvent and a vehicle.

Other chemicals, referred to herein simply as additives, can also beincluded in the low viscosity precursor compositions of the presentinvention. As is discussed below, such additives can include, but arenot limited to, crystallization inhibitors, polymers, polymer precursors(oligomers or monomers), reducing agents, binders, dispersants,surfactants, humectants, defoamers and the like.

Precursor Compositions

As is discussed above, the low viscosity precursor compositionsaccording to the present invention can optionally include particulatesin the form of nanoparticles and/or micron-size particles.

Nanoparticles have an average size of not greater than about 100nanometers, such as from about 10 to 80 nanometers. Particularlypreferred for low viscosity precursor compositions are nanoparticleshaving an average size in the range of from about 25 to 75 nanometers.

Nanoparticles that are particularly preferred for use in the presentinvention are not substantially agglomerated. Preferred nanoparticlecompositions include Al₂O₃, CuO_(x), SiO₂ and TiO₂, conductive metaloxides such as In₂O₃, indium-tin oxide (ITO) and antimony-tin oxide(ATO), silver, palladium, copper, gold, platinum and nickel. Otheruseful nanoparticles of metal oxides include pyrogenous silica such asHS-5 or M5 or others (Cabot Corp., Boston, Mass.) and AEROSIL 200 orothers (Degussa AG, Dusseldorf, Germany) or surface modified silica suchas TS530 or TS720 (Cabot Corp., Boston, Mass.) and AEROSIL 380 (DegussaAG, Dusseldorf, Germany). In one embodiment of the present invention,the nanoparticles are composed of the same metal that is contained inthe metal precursor compound, discussed below. Nanoparticles can befabricated using a number of methods and one preferred method, referredto as the Polyol process, is disclosed in U.S. Pat. No. 4,539,041 byFiglarz et al., which is incorporated herein by reference in itsentirety.

The precursor compositions according to the present invention can alsoinclude micron-size particles, having an average size of at least about0.1 μm. Preferred compositions of micron-size particles are similar tothe compositions described above with respect to nanoparticles. Theparticles are preferably spherical, such as those produced by spraypyrolysis. Particles in the form of flakes increase the viscosity of theprecursor composition and are not amenable to deposition using toolshaving a restricted orifice size, such as an ink-jet device. Whensubstantially spherical particles are described herein, the particlesize refers to the particle diameter. In one preferred embodiment, thelow viscosity precursor compositions according to the present inventiondo not include any particles in the form of flakes.

Generally, the volume median particle size of the micron-size particlesutilized in the low viscosity precursor compositions according to thepresent invention is at least about 0.1 μm, such as at least about 0.3μm. Further, the volume median particle size is preferably not greaterthan about 20 μm. For most applications, the volume median particle sizeis more preferably not greater than about 10 μm and even more preferablyis not greater than about 5 μm. A particularly preferred median particlesize for the micron-size particles is from about 0.3 μm to about 3 μm.According to one embodiment of the present invention, it is preferredthat the volume median particle size of the micron-size particles is atleast 10 times smaller than the orifice diameter in the tool using thecomposition, such as not greater than about 5 gm for an ink-jet headhaving a 50 μm orifice.

There are many difficulties typically associated with depositing lowviscosity compositions containing particulates. If many of theparticulates are too small in size (nanoparticles), the viscosity of thecomposition can be too high. At the other extreme, larger micron-sizeparticles tend to settle quickly out of the liquid leading to a shortshelf life for the suspensions. Larger particles and particleagglomerates also tend to clog the orifices of many direct-write toolssuch as syringes and ink-jets. Flakes do not flow as easily throughnarrow channels and therefore spherical particulates are preferred.However, spherical particles of many materials are not readilyavailable. For these and other reasons, many electronic materials havenot been readily deposited using such direct-write tools.

The micron-size particles that are useful in the precursor compositionsof the present invention advantageously have settling velocities thatcorrespond to relatively small particle sizes when measured by asedimentation technique, corresponding to porous or hollow particles.There are numerous ways to measure and quantify particle size includingby mass, volume and number. For the low viscosity compositions of thepresent invention, one of the most important aspects is that theparticles do not settle rapidly and the means by which the particle sizeis measured and reported must be carefully interpreted in this context.The geometric sizes of the particles, as might be observed using amicroscope, do not reflect that particles with the same size can havedifferent densities and therefore significantly different settlingvelocities. Hollow or porous micron-size particles settle more slowlythan dense particles. Similarly, optically determined particle sizes asfrom light scattering in liquids or gases also provide data that onlyreflect the geometric size of the particles and these measurements donot reflect that particles of the same size can have differentdensities. Any measurement that provides the actual physical size of theparticles, such as optical techniques, can provide numbers that must beinterpreted with caution. For-example, the volume median diameter ofparticles determined from light scattering cannot easily be related tomass median diameter in the absence of information about the apparentdensity of the particles, such as whether they are hollow or porous andthe extent of the porosity. Likewise, the particle size data determinedfrom settling velocities can provide information about the settlingbehavior of the particles, but does not provide information about thetrue geometric particle size if the particles are hollow or porous.

However, the combination of size data measured from optically-basedapproaches and data measured from sedimentation velocity provides ameasure of particle performance in low viscosity compositions, wherecontrol of the particle settling rate is crucial. A small sizecalculated from settling velocity of a dense particle along with a largegeometric size is an indication of hollow or porous particles. It ispreferred that the average size of the micron-size particles utilized inthe precursor compositions of the present invention, as measured bysedimentation techniques corresponds to dense particles having asettling velocity corresponding to an average particle size of notgreater than about 4 μm, more preferably not greater than about 1 μm,even more preferably not greater than about 0.5 μm and even morepreferably not greater than about 0.1 μm.

Thus, the micron-size particles according to the present inventionpreferably include particles having a low settling rate as measured bysettling techniques while having a larger size when measured bygeometric techniques. One such geometric technique is to measure theparticle size by light scattering using a MICROTRAC particle sizeanalyzer (Honeywell Industrial Automation and Control, Fort Washington,Pa.), which yields a geometric (volume) average particle size.

It is desirable to maintain a substantially neutral buoyancy of themicron-size particles in the suspension while maintaining a relativelylarge physical size. The buoyancy is required for stability while thelarger size maintains liquid properties, such as viscosity or lightscattering ability, within useful ranges. Stated another way, it isoften desirable to provide micron-size particles having a low settlingvelocity but at high loadings. The settling velocity of the particles isproportional to the apparent density of the particle (ρ_(p)) minus thedensity of the liquid (ρ_(L)). Ideally, the particles will have anapparent density that is approximately equal to the density of theliquid, which is typically about 1 g/cm³ (e.g., the density of water).Since a typical metal has a theoretical density in the range of fromabout 6 to about 20 g/cm³, it is preferable that the apparent density ofsuch micron-size particles be a fraction of the theoretical density.According to one embodiment, the micron-size particles have an apparentdensity that is not greater than about 75 percent of the theoreticaldensity for the particle, more preferably not greater than about 50percent of the theoretical density.

One preferred method for obtaining a reduced apparent density of themicron-size particles according to the present invention is to produceparticles having a hollow microstructure. That is, one preferredparticle morphology is a particle comprised of a dense shell having aninner radius and an outer radius. Preferably, the shell has a highdensity and is substantially impermeable. For such a hollow particle,the equation representing the conditions for neutral buoyancy can bewritten:$r_{2} = {\left\lbrack \sqrt[3]{\frac{\rho_{p}}{\rho_{p} - 1}} \right\rbrack r_{1}}$

where:

-   -   r₁=inner radius        -   ρ_(L)=(water)    -   r₂=outer radius    -   ρ_(p)=theoretical density of the particle

For example, if a hollow particle has an outer radius of 2 μm (4 μmdiameter) and a density of 5 g/cm³, then the optimum average wallthickness would be about 0.15 μm for the particle to be neutrallybuoyant in a liquid having a density of 1 g/cm³.

Although hollow micron-size particles can be preferred according to thepresent invention, it will be appreciated that other particlemorphologies can be utilized while maintaining an apparent densitywithin the desired range. For example, the particles could have asufficient amount of closed porosity to yield a particle having anapparent density that is lower than the theoretical density. Open(surface) porosity can also decrease the apparent density if the surfacetension of the liquid medium (the liquid precursor components) does notenable the liquid to substantially penetrate the surface pores. Forexample, supported electrocatalyst particles, such as those disclosed inU.S. Pat. No. 6,103,393 by Kodas et al., can have a high level ofporosity and surface area.

Thus, the particles that are particularly useful in low viscosityprecursor compositions according to the present invention have a lowsettling velocity in the liquid medium. The settling velocity accordingto Stokes Law can be defined as:$V = \frac{{D_{st}^{2}\left( {\rho_{s} - \rho_{l}} \right)}g}{18\eta}$

where:

-   -   D_(st)=Stokes diameter    -   η=fluid viscosity    -   ρ_(s)=apparent density of the particle    -   p₁=density of the liquid    -   V=settling velocity    -   g=acceleration due to gravity

Preferably, the average settling velocity of the particles issufficiently low such that the precursor compositions have a usefulshelf life without the necessity of mechanical mixing techniques. Thus,it is preferred that a large mass fraction of the particles, such as atleast about 50 weight percent remains suspended in the liquid for atleast 1 hour. Stated another way, the micron-size particles preferablyhave a settling velocity that is not greater than 50 percent, morepreferably not greater than 20 percent, of a theoretically denseparticle of the same composition. Further, the particles can becompletely redispersed after settling, such as by mixing, to provide thesame particle size distribution in suspension as measured beforesettling.

According to a preferred embodiment of the present invention, theparticles (nanoparticles and micron-size particles) also have a narrowparticle size distribution, such that the majority of particles areabout the same size and so that there are a minimal number of largeparticles that can clog an orifice, such as an orifice in an ink-jethead. A narrow particle size distribution is particularly advantageousfor direct-write applications due to reduced clogging of the orifice bylarge particles and due to the ability to form surface features-having-afine line width, high resolution and high packing density. Preferably,at least about 70 volume percent and more preferably at least about 80volume percent of the particles within the same size classification(nanoparticles or micron-size particles) are not larger than twice theaverage particle size. For example, when the average particle size ofmicron-size particles is about 2 μm, it is preferred that at least about70 volume percent of the micron-size particles are not larger than 4 μmand it is more preferred that at least about 80 volume percent of themicron-size particles are not larger than 4 μm. Further, it is preferredthat at least about 70 volume percent and more preferably at least about80 volume percent of the particles are not larger than about 1.5 timesthe average particle size. Thus, when the average particle size of themicron-size particles is about 2 μm, it is preferred that at least about70 volume percent of the micron-size particles are not larger than 3 μmand it is more preferred that at least about 80 volume percent of themicron-size particles are not larger than 3 μm.

It is known that micron-size particles and nanoparticles often form softagglomerates as a result of their relatively high surface energies, ascompared to larger particles. It is also known that such softagglomerates may be dispersed easily by treatments such as exposure toultrasound in a liquid medium, sieving, high shear mixing and 3-rollmilling. The average particle size and particle size distributionsdescribed herein are measured by mixing samples of the powders in aliquid medium, such as water and a surfactant, and exposing thesuspension to ultrasound through either an ultrasonic bath or horn. Theultrasonic treatment supplies sufficient energy to disperse the softagglomerates into primary particles. The primary particle size and sizedistribution are then measured by light scattering in a MICROTRACinstrument. This provides a good measure of the usefull dispersioncharacteristics of the powder because this simulates the dispersion ofthe particles in a liquid vehicle, such as an ink-jet suspension. Thus,the references to particle size herein refer to the primary particlesize, such as after lightly dispersing soft agglomerates of theparticles.

It is also possible to provide micron-size particles or nanoparticleshaving a bimodal particle size distribution. That is, the particles canhave two distinct and different average particle sizes. Preferably, eachof the distinct particle size distributions will meet the foregoing sizedistribution limitations. A bimodal or trimodal particle sizedistribution can advantageously enhance the packing efficiency of theparticles when deposited according to the present invention. In oneembodiment, the larger mode includes hollow or porous particles whilethe smaller mode includes dense particles. The two modes can includeparticles of different composition. In one embodiment, the two modeshave average particle sizes at about 1 μm and 5μm, and in anotherembodiment the average particle size of the 2 modes is about 0.5 μm and2.5 μm. The bimodal particle size distribution can also be achievedusing nanoparticles and in one embodiment the larger mode has an averageparticle size of from about 1 μm to 10 μm and the smaller mode has anaverage particle size of from about 10 to 100 nanometers.

The particles that are useful in precursor compositions according to thepresent invention also preferably have a high degree of purity and it ispreferred that the particles include not greater than about 1.0 atomicpercent impurities and more preferably not greater than about 0.1 atomicpercent impurities and even more preferably not greater than about 0.01atomic percent impurities. Impurities are those materials that are notintended in the final product (i.e., the conductive feature) and thatnegatively affect the properties of the final product. For manyelectronic applications, the most critical impurities to avoid are Na,K, Cl, S and F. As is discussed below, it will be appreciated that theparticles can include composite particles having one or more secondphases. Such second phases are not considered impurities.

The particles for use in the precursor compositions according to thepresent invention can also be coated particles wherein the particleincludes a surface coating surrounding the particle core. Coatings canbe generated on the particle surface by a number of differentmechanisms. One preferred mechanism is spray pyrolysis. One or morecoating precursors can vaporize and fuse to the hot particle surface andthermally react resulting in the formation of a thin film coating bychemical vapor deposition (CVD). Preferred coatings deposited by CVDinclude metal oxides and elemental metals. Further, the coating can beformed by physical vapor deposition (PVD) wherein a coating materialphysically deposits on the surface of the particles. Preferred coatingsdeposited by PVD include organic materials and elemental metals.Alternatively, a gaseous precursor can react in the gas phase formingsmall particles, for example, less than about 5 nanometers in size,which then diffuse to the larger particle surface and sinter onto thesurface, thus-forming a coating. This method is referred to asgas-to-particle conversion (GPC). Whether such coating-reactions occurby CVD, PVD or GPC is dependent on the reactor conditions, such astemperature, precursor partial pressure, water partial pressure and theconcentration of particles in the gas stream. Another possible surfacecoating method is surface conversion of the particles by reaction with avapor phase reactant to convert the surface of the particles to adifferent material than C that originally contained in the particles.

In addition, a volatile coating material such as lead oxide, molybdenumoxide or vanadium oxide can be introduced into the reactor such that thecoating deposits on the particles by condensation. Further, theparticles can be coated using other techniques. For example, solubleprecursors to both the particle and the coating can be used in theprecursor solution. In another embodiment, a colloidal precursor and asoluble precursor can be used to form a particulate colloidal coating onthe composite particle. It will be appreciated that multiple coatingscan be deposited on the surface of the particles if such multiplecoatings are desirable.

The coatings are preferably as thin as possible while maintainingconformity about the particles such that the core of the particle is notsubstantially exposed. For example, the coatings on a micron-sizeparticle can have an average thickness of not greater than about 200nanometers, preferably not greater than about 100 nanometers and morepreferably not more than about 50 nanometers. For most applications, thecoating has an average thickness of at least about 5 nanometers. Aspecific example of useful coated particles is silica coated silverparticles.

Nanoparticles can also be coated by utilizing the coating strategies asdescribed above. In addition, it may be advantageous to coatnanoparticles with materials such as a polymer, to prevent agglomerationof the nanoparticles due to high surface energy. This is described by P.Y. Silvert et al. (Preparation of colloidal silver dispersions by thepolyol process, Journal of Material Chemistry, 1997, volume 7(2), pp.293-299). In another embodiment, the particles can be coated with anintrinsically conductive polymer, preventing agglomeration in thecomposition and providing a conductive patch after solidification of thecomposition. In yet another embodiment, the polymer can decompose duringheating enabling the nanoparticles to sinter together. In oneembodiment, the nanoparticles are generated in-situ and are coated witha polymer. Preferred coatings for nanoparticles according to the presentinvention include sulfonated perfluorohydrocarbon polymer (e.g., NAFION,available from E.I. duPont deNemours, Wilmington, Del.), polystyrene,polystyrene/methacrylate, polyvinyl pyrolidone, sodium bis(2-ethylhexyl)sulfosuccinate, tetra-n-octyl-ammonium bromide and alkane thiolates.

The particles that are useful with the present invention can also be“capped” with other compounds. The term capped refers to havingcompounds bonded to the outer surface of the particles withoutnecessarily creating a coating over the outer surface. The particlesused with the present invention can be capped with any functional groupincluding organic compounds such as polymers, organometallic compounds,and metal organic compounds. These capping agents can serve a variety offunctions including the prevention of agglomeration of the particles,prevention of oxidation, enhancement of bonding of the particles to asurface, and enhancement of the flowability of the particles in aprecursor composition. Preferred capping agents that are useful with theparticles of the present invention include amine compounds,organometallic compounds, and metal organic compounds.

The particulates in accordance with the present invention can also becomposite particles wherein the particles include a first phase and asecond phase associated with the first phase. Preferred compositeparticulates include carbon-metal, carbon-polymer, carbon-ceramic,carbon1-carbon2, ceramic-ceramic, ceramic-metal, metal1-metal2,metal-polymer, ceramic-polymer, and polymer1-polymer2. Also preferredare certain 3-phase combinations such as metal-carbon-polymer. In oneembodiment, the second phase is uniformly dispersed throughout the firstphase. The second phase can be an electronic compound or it can be anon-electronic compound. For example, sintering inhibitors such as metaloxides can be included as a second phase in a first phase of a metallicmaterial, such as silver metal to inhibit sintering of the metal withoutsubstantially affecting the conductivity.

As a further example, the particles can be electrocatalyst particles,such as those composed of a metal or a metal oxide dispersed on asupport such as carbon. Such particles are disclosed in U.S. Pat. No.6,103,393 by Kodas et al., which is incorporated herein by reference inits entirety. Such particles can be used in fuel cells such as directmethanol fuel cells (DMFC) and proton exchange membrane fuel cells(PEMFC), as well as metal-air batteries and similar devices.

Further, the micron-size particles can be hollow particles, as isdiscussed above; wherein the shell includes a first phase and a secondphase dispersed throughout the first phase.

The particulates according to a preferred embodiment of the presentinvention are also substantially spherical in shape. That-is, theparticulates are not jagged or irregular in shape. Spherical particlesare particularly advantageous because they are able to disperse morereadily in a liquid suspension and impart advantageous flowcharacteristics to the precursor composition, particularly fordeposition using an ink-jet device or similar tool. For a given level ofsolids loading, a low viscosity precursor composition having sphericalparticles will have a lower viscosity than a composition havingnon-spherical particles, such as flakes. Spherical particles are alsoless abrasive than jagged or plate-like particles, reducing the amountof abrasion and wear on the deposition tool.

Thus, micron-size particles with low settling densities derived fromtheir porosity or hollowness can be used to provide the low viscosityprecursor compositions. Such micron-size particles can be produced, forexample, by spray pyrolysis. Spray pyrolysis for production ofmicron-size particles is described in U.S. Pat. No. 6,103,393 by Kodas,et al., which is incorporated herein by reference in its entirety.

Hollow particles with well-controlled apparent density canadvantageously be formed by the spray-pyrolysis process disclosed above.In the case of metals such as silver, it is often necessary to add smallamounts of metal oxide precursors, or salts to the starting solutionthat can be removed after particle formation. The metal oxides or thesalts inhibit the densification of the metal particles during theresidence time in the reactor. As an example, porous and/or hollowparticles of conductors with reduced density can be formed by addingmetal oxide precursors such as alumina, silica, copper oxides, glasses(e.g., barium aluminum borosilicate, calcium silicate or leadborosilicate) and virtually any other metal oxide that has a meltingpoint significantly greater than the metal. These additives can alsoserve the dual purpose of providing adhesion to substrates, inhibitingsintering (as in the case of silver that has a low sinteringtemperature), modifying temperature coefficients of resistivity andother functions.

Another method for providing hollow particles in a spray pyrolysisprocess is the use of particle precursors having low solubility.Precursors having a low solubility precipitate at the surface of thedroplet thereby-forming a shell. As the remainder of the solvent leaves,more metal precursor precipitates onto the shell, forming a hollowparticle. Examples include organometallics, metal organics and inorganicprecursors. Preferred particle precursors according to this embodimenthave solubilities of not greater than about 20 wt. %, more preferablynot greater than about 10 wt. % and even more preferably not greaterthan about 5 wt. %. Inorganic precursors can be selected, for example,from metal nitrates, metal halides, metal sulfates, metal hydroxides andmetal carbonates.

Another method for forming hollow particles is to use particleprecursors that have low effective yields during conversion from theprecursor to the particulate product. Once the droplets are dried andthe particles consist only of precursor, reaction to form the productresults in a porous or hollow particle because of the large volumechange from reactant to product with a relatively constant particlediameter. One example is the formation of alumina from aluminum nitrate.Preferred particle precursors according to this embodiment have avolumetric yield of not greater than about 50%, more preferably notgreater than about 25% and even more preferably not greater than about10%.

Another method is to use particle precursors that liberate gases andinflate the particles during reaction of the precursor. Preferredparticle precursors according to this embodiment release, for example,NO_(x) or CO₂ gas.

Metal salts such as nitrates, chlorides, sulfates, hydroxides oroxalates can be used as particle precursors in a spray pyrolysisprocess. Preferred metal salts include the metal nitrates. For example,a preferred precursor to platinum metal according to the presentinvention is nitrated diammine dinitroplatinum (II). Another preferredmetal is silver and a preferred precursor to silver metal particles issilver nitrate, AgNO₃, or a silver carboxylate compound.

The precursor compositions according to the present invention can alsoinclude molecular metal precursors, either alone or in combination withparticulates. Preferred examples include molecular metal precursors tosilver (Ag), nickel (Ni), platinum (Pt), gold (Au), palladium (Pd),copper (Cu), indium (In) and tin (Sn). Other molecular metal precursorscan include precursors to aluminum (Al), zinc (Zn), iron (Fe), tungsten(W), molybdenum (Mo), ruthenium (Ru), lead (Pb), bismuth (Bi) andsimilar metals. The molecular metal precursors can be either soluble orinsoluble;in the precursor composition.

In general, molecular metal precursor compounds that eliminate ligandsby a radical mechanism upon conversion to metal are preferred,especially if the species formed are stable radicals and therefore lowerthe decomposition temperature of that precursor compound.

Furthermore, molecular metal precursors containing ligands thateliminate cleanly upon precursor conversion and escape completely fromthe substrate (or the formed functional structure) are preferred becausethey are not susceptible to carbon contamination or contamination byanionic species such as nitrates. Therefore, preferred precursors formetals used for conductors are carboxylates, alkoxides or combinationsthereof that would convert to metals, metal oxides or mixed metal oxidesby eliminating small molecules such as carboxylic acid anhydrides,ethers or esters. Metal carboxylates, particularly halogenocarboxylatessuch as fluorocarboxylates, are particularly preferred metal precursorsdue to their high solubility.

Particularly preferred metal precursor compounds are metal precursorcompounds containing silver, nickel, platinum, gold, palladium, copperand ruthenium.

Examples of silver metal precursors that can be used in the lowviscosity precursor compositions according to the present invention areillustrated in Table 1. TABLE 1 Silver Precursor Molecular Compounds andSalts General Class Examples Chemical Formula Nitrates Silver nitrateAgNO₃ Nitrites Silver nitrite AgNO₂ Oxides Silver oxide Ag₂O, AgOCarbonates Silver carbonate Ag₂CO₃ Oxalates Silver oxalate Ag₂C₂O₄(Pyrazolyl)borates Silver trispyrazolylborate Ag[(N₂C₃H₃)₃]BH Silvertris(dimethylpyrazolyl)borate Ag[((CH₃)₂N₂C₃H₃)₃]BH Azides Silver azideAgN₃ Fluoroborates Silver tetrafluoroborate AgBF₄ Carboxylates Silveracetate AgO₂CCH₃ Silver propionate AgO₂CC₂H₅ Silver butanoate AgO₂CC₃H₇Silver ethylbutyrate AgO₂CCH(C₂H₅)C₂H₅ Silver pivalate AgO₂CC(CH₃)₃Silver cyclohexanebutyrate AgO₂C(CH₂)₃C₆H₁₁ Silver ethylhexanoateAgO₂CCH(C₂H₅)C₄H₉ Silver neodecanoate AgO₂CC₉H₁₉ HalogenocarboxylatesSilver trifluoroacetate AgO₂CCF₃ Silver pentafluoropropionate AgO₂CC₂F₅Silver heptafluorobutyrate AgO₂CC₃F₇ Silver trichloroacetate AgO₂CCCl₃Silver 6,6,7,7,8,8,8-heptafluoro-2,2- AgFOD dimethyl-3,5-octanedionateHydroxycarboxylates Silver lactate AgO₂CH(OH)CH₃ Silver citrateAg₃C₆H₅O₇ Silver glycolate AgOOCCH(OH)CH₃ Aminocarboxylates Silverglyconate Aromatic and nitro and/or Silver benzoate AgO₂CCH₂C₆H₅ fluorosubstituted aromatic Silver phenylacetate AgOOCCH₂C₆H₅ CarboxylatesSilver nitrophenylacetates AgOOCCH₂C₆H₄NO₂ Silver dinitrophenylacetateAgOOCCH₂C₆H₃(NO₂)₂ Silver difluorophenylacetate AgOOCCH₂C₆H₃F₂ Silver2-fluoro-5-nitrobenzoate AgOOCC₆H₃(NO₂)F Beta diketonates Silveracetylacetonate Ag[CH₃COCH═C(O—)CH₃] Silver hexafluoroacetylacetonateAg[CF₃COCH═C(O—)CF₃] Silver trifluoroacetylacetonateAg[CH₃COCH═C(O—)CF₃] Silver sulfonates Silver tosylate AgO₃SC₆H₄CH₃Silver triflate AgO₃SCF₃

In addition to the foregoing, complex silver salts containing neutralinorganic or organic ligands can also be used as precursors. These saltsare usually in the form of nitrates, halides, perchlorates, hydroxidesor tetrafluoroborates. Examples are listed in Table 2. TABLE 2 ComplexSilver Salt Precursors Class Examples (Cation) Amines [Ag(RNH₂)₂]⁺,Ag(R₂NH)₂]⁺, [Ag(R₃N)₂]⁺, R = aliphatic or aromatic N-Heterocycles[Ag(L)_(x)]⁺, (L = aziridine, pyrrol, indol, piperidine, pyridine,aliphatic substituted and amino substituted pyridines, imidazole,pyrimidine, piperazine, triazoles, etc.) Amino alcohols [Ag(L)_(x)]⁺, L= Ethanolamine Amino acids [Ag(L)_(x)]⁺, L = Glycine Acid amides[Ag(L)_(x)]⁺, L = Formamides, acetamides Nitriles [Ag(L)_(x)]⁺, L =Acetonitriles

The molecular metal precursors can be utilized in an aqueous-basedsolvent or an organic solvent. Organic solvents are typically used forink-jet deposition. Preferred molecular metal precursors for silver inan organic solvent include Ag-nitrate, Ag-neodecanoate,Ag-trifluoroacetate, Ag-acetate, Ag-lactate, Ag-cyclohexanebutyrate,Ag-carbonate, Ag-oxide, Ag-ethylhexanoate, Ag-acetylacetonate,Ag-ethylbutyrate, Ag-pentafluoropropionate, Ag-benzoate, Ag-citrate,Ag-heptafluorobutyrate, Ag-salicylate, Ag-decanoate and Ag-glycolate.Among the foregoing, particularly preferred molecular metal precursorsfor silver include Ag-acetate, Ag-nitrate, Ag-trifluoroacetate andAg-neodecanoate. Most preferred among the foregoing silver precursorsare Ag-trifluoroacetate and Ag-acetate. The preferred precursorsgenerally have a high solubility and high metal yield. For example,Ag-trifluoroacetate has a solubility in dimethylacetamide (DMAc) ofabout 78 wt. % and Ag-trifluoroacetate is a particularly preferredsilver precursor according to the present invention.

Preferred molecular silver precursors for aqueous-based solvents includeAg-nitrates, Ag-fluorides such as silver fluoride or silver hydrogenfluoride (AgHF₂), Ag-thiosulfate, Ag-trifluoroacetate and solublediammine complexes of silver salts.

Silver precursors in solid form that decompose at a low temperature,such as not greater than about 200° C., can also be used. Examplesinclude Ag-oxide, Ag-nitrite, Ag-carbonate, Ag-lactate, Ag-sulfite andAg-citrate.

When a more volatile molecular silver precursor is desired, such as forspray deposition of the precursor composition, the precursor can beselected from alkene silver betadiketonates, R₂(CH)₂Ag([R′COCH═C(O—)CR″]where R=methyl or ethyl and R′, R″═CF₃, C₂F₅, C₃F₇, CH₃,C_(m)H_(2m+)(m=2 to 4), or triarylphosphine and triarylphosphinederivatives of silver carboxylates, silver beta diketonates or silvercyclopentadienides.

Molecular metal precursors for nickel that are preferred according tothe present invention are illustrated in Table 3. A particularlypreferred nickel precursor for use with an aqueous-based solvent isNi-acetylacetonate. TABLE 3 Molecular Metal Precursors for NickelGeneral Class Example Chemical Formula Inorganic Salts Ni-nitrateNi(NO₃)₂ Ni-sulfate NiSO₄ Nickel ammine [Ni(NH₃)₆]^(n+) (n = 2,3)complexes Ni-tetrafluoroborate Ni(BF₄)₂ Metal Organics Ni-oxalate NiC₂O₄(Alkoxides, Beta- Ni-isopropoxide Ni(OC₃H₇)₂ diketonates,Ni-methoxyethoxide Ni(OCH₂CH₂OCH₃)₂ Carboxylates, Ni-acetylacetonate[Ni(acac)₂]₃ or Ni(acac)₂(H₂O)₂ Fluoro- Ni-hexafluoro-Ni[CF₃COCH═C(O—)CF₃]₂ carboxylates acetylacetonate Ni-formate Ni(O₂CH)₂Ni-acetate Ni(O₂CCH₃)₂ Ni-octanoate Ni(O₂CC₇H₁₅)₂ Ni-ethylhexanoateNi(O₂CCH(C₂H₅)C₄H₉)₂ Ni-trifluoroacetate Ni(OOCCF₃)₂

Various molecular precursors can be used for platinum metal. Preferredmolecular precursors include ammonium salts of platinates such asammonium hexachloro platinate (NH₄)₂PtCl₆, and ammonium tetrachloroplatinate (NH₄)₂PtCl₄; sodium and potassium salts of halogeno,pseudohalogeno or nitrito platinates such as potassium hexachloroplatinate K₂PtCl₆, sodium tetrachloro platinate Na₂PtCl₄, potassiumhexabromo platinate K₂PtBr₆, potassium tetranitrito platinateK₂Pt(NO₂)₄; dihydrogen salts of hydroxo or halogeno platinates such ashexachloro platinic acid H₂PtCl₆, hexabromo platinic acid H₂PtBr₆,dihydrogen hexahydroxo platinate H₂Pt(OH)₆; diammine and tetraammineplatinum compounds such as diammine platinum chloride Pt(NH₃)₂Cl₂,tetraammine platinum chloride [Pt(NH₃)₄]Cl₂, tetraammine platinumhydroxide [Pt(NH₃)₄](OH)₂, tetraammine platinum nitrite[Pt(NH₃)₄](NO₂)₂, tetrammine platinum nitrate Pt(NH₃)₄(NO₃)₂, tetrammineplatinum bicarbonate [Pt(NH₃)₄](HCO₃)₂, tetraammine platinumtetrachloroplatinate [Pt(NH₃)₄]PtCl4; platinum diketonates such asplatinum (II) 2,4-pentanedionate Pt(C₅H₇O₂) ₂; platinum nitrates such asdihydrogen hexahydroxo platinate H₂Pt(OH)₆ acidified with nitric acid;other platinum salts such as Pt-sulfite and Pt-oxalate; and platinumsalts comprising other N-donor ligands such as [Pt(CN)₆]⁴⁺.

Platinum precursors useful in organic-based precursor compositionsinclude Pt-carboxylates or mixed carboxylates. Examples of carboxylatesinclude Pt-formate, Pt-acetate, Pt-propionate, Pt-benzoate, Pt-stearate,Pt-neodecanoate. Other precursors useful in organic vehicles includeaminoorgano platinum compounds includingPt(diaminopropane)(ethylhexanoate).

Preferred combinations of platinum precursors and solvents include:PtCl₄ in H₂O; Pt-nitrate solution from H₂Pt(OH)₆; H₂Pt(OH)₆ in H₂O;H₂PtCl₆ in H₂O; and [Pt(NH₃)₄](NO₃)₂ in H₂O.

Gold precursors that are particularly useful for aqueous based precursorcompositions include Au-chloride (AuCl₃) and tetrachloric auric acid(HAuCl₄).

Gold precursors useful for organic based formulations include:Au-thiolates, Au-carboxylates such as Au-acetate Au(O₂CCH₃)₃;aminoorgano gold carboxylates such as imidazole gold ethylhexanoate;mixed gold carboxylates such as gold hydroxide acetate isobutyrate;Au-thiocarboxylates and Au-dithiocarboxylates.

In general, preferred gold molecular metal precursors for lowtemperature conversion are compounds comprising a set of differentligands such as mixed carboxylates or mixed alkoxo metal carboxylates.As one example, gold acetate isobutyrate hydroxide decomposes at 155°C., a lower temperature than gold acetate. As another example, goldacetate neodecanoate hydroxide decomposes to gold metal at even lowertemperature, 125° C. Still other examples can be selected from goldacetate trifluoroacetate hydroxide, gold bis(trifluoroacetate) hydroxideand gold acetate pivalate hydroxide.

Other useful gold precursors include Au-azide and Au-isocyanide. When amore volatile molecular gold precursor is desired, such as for spraydeposition, the precursor can be selected from:

-   -   dialkyl and monoalkyl gold carboxylates, R_(3−n)Au(O₂CR′)_(n)        (n=1,2) R=methyl, ethyl; R′═CF₃, C₂F₅, C₃F₇, CH₃, C_(m)H_(2m+1)        (m=2-9)    -   dialkyl and monoalkyl gold beta diketonates, R_(3-n)Au        [R′COCH═C(O-)CR″]_(n) (n=1,2), R=methyl, ethyl; R′, R″═CF₃,        C₂F₅, C₃F₇, CH₃, C_(m)H_(2m+1) (m=2-4)    -   dialkyl and monoalkyl gold alkoxides, R_(3−n)Au(OR′)_(n) (n=1,2)        R=methyl, ethyl; R′═CF₃, C₂F₅, C₃F₇, CH₃, C_(m)H_(2m+1) (m=2-4),        SiR₃″(R″=methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,        tert. Butyl)    -   phosphine gold complexes:        -   RAu(PR′₃) R, R′=methyl, ethyl, propyl, isopropyl, n-butyl,            isobutyl, tert. butyl.,

R₃Au(PR′₃) R, R′=methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,tert. butyl.

Particularly usefull molecular precursors to palladium for organic basedprecursor compositions according to the present invention includePd-carboxylates, including Pd-fluorocarboxylates such as Pd-acetate,Pd-propionate, Pd-ethylhexanoate, Pd-neodecanoate andPd-,trifluoroacetate as well as mixed carboxylates such asPd(OOCH)(OAc), Pd(OAc)(ethylhexanoate), Pd(ethylhexanoate)₂,Pd(OOCH)_(1.5) (ethylhexanoate)_(0.5), Pd(OOCH)(ethylhexanoate),Pd(OOCCH(OH)CH(OH)COOH)_(m) (ethylhexanoate), Pd(OPr)₂, Pd(OAc)(OPr),Pd-oxalate, Pd(OOCCHO)_(m)(OOCCH₂OH)_(n) =(Glyoxilic palladiumglycolate) and Pd-alkoxides. A particularly preferred palladiumprecursor is Pd-trifluoroacetate.

Palladium precursors useful for aqueous based precursor compositionsinclude: tetraammine palladium hydroxide [Pd(NH₃)₄](OH)₂; Pd-nitratePd(NO₃)₂; Pd-oxalate Pd(O₂CCO₂)₂; Pd-chloride PdCl₂; Di- and tetraamminepalladium chlorides, hydroxides or nitrates such as tetraamminepalladium chloride [Pd(NH₃)₄]Cl₂, tetraammine palladium hydroxide[Pd(NH₃)₄](OH)₂, tetraammine palladium nitrate [Pd(NH₃)₄](NO₃)₂,diammine palladium nitrate [Pd(NH₃)₂](NO₃)₂ and tetraammine palladiumtetrachloropalladate [Pd(NH₃)₄][PdCl₄].

When selecting a molecular copper precursor compound, it is desired thatthe compound react during processing to metallic copper without theformation of copper oxide or other species that are detrimental to theconductivity of the conductive copper feature. Some copper molecularprecursors form copper by thermal decomposition at elevatedtemperatures. Other molecular copper precursors require a reducing agentto convert to copper metal. Reducing agents are materials that areoxidized, thereby causing the reduction of another substance. Thereducing agent loses one or more electrons and is referred to as havingbeen oxidized. The introduction of the reducing agent can occur in theform of a chemical agent (e.g., formic acid) that is soluble in theprecursor composition to afford a reduction to copper either duringtransport to the substrate or on the substrate. In some cases, theligand of the molecular copper precursor has reducing characteristics,such as in Cu-formate or Cu-hypophosphite, leading to reduction tocopper metal. However, formation of metallic copper or other undesiredside reactions that occur prematurely in the ink or precursorcomposition should be avoided.

Accordingly, the ligand can be an important factor in the selection ofsuitable copper molecular precursors. During thermal decomposition orreduction of the precursor, the ligand needs to leave the systemcleanly, preferably without the formation of carbon or other residues itcould be incorporated into the copper feature. Copper precursorscontaining inorganic ligands are preferred in cases where carboncontamination is detrimental. Other desired characteristics formolecular copper precursors are low decomposition temperature orprocessing temperature for reduction to copper metal, high solubility inthe selected solvent/vehicle to increase metallic yield and achievedense features and the compound should be environmentally benign.

Preferred copper metal precursors according to the present inventioninclude Cu-formate and Cu-neodecanoate. Molecular copper precursors thatare useful for aqueous-based precursor compositions include: Cu-nitrateand ammine complexes thereof; Cu-carboxylates including Cu-formate andCu-acetate; and Cu beta-diketonates such as Cu-hexafluoroacetylacetonateand copper salts such as Cu-chloride.

Molecular copper precursors generally useful for organic basedformulations include: Cu-carboxylates and Cu-fluorocarboxylates, such asCu-formate; Cu-ethylhexanoate; Cu-neodecanoate; Cu-methacrylate;Cu-trifluoroacetate; Cu-hexanoate; and copper beta-diketonates such ascyclooctadiene Cu hexafluoroacetylacetonate.

Among the foregoing, Cu-formate is particularly preferred as it ishighly soluble in water and results in the in-situ formation of formicacid, which is an effective reducing agent.

Copper precursors useful in this invention can also be categorized ascopper I and copper II compounds. They can be categorized as inorganic,metal organic, and organometallic. They can also be categorized ascopper hydrides, copper amides, copper alkenes, copper allyls, coppercarbonyls, copper metallocenes, copper cyclopentadienyls, copper arenes,copper carbonates, copper hydroxides, copper carboxylates, copperoxides, organo copper, copper beta-diketonates, copper alkoxides, copperbeta-ketoiminates, copper halides, copper alkyls. The copper compoundscan have neutral donor ligands or not have neutral ligands. Copper Icompounds are particularly useful for, disproportionation reactions. Thedisproportionation products are copper metal and a copper II compound.In some cases a neutral ligand is also a product.

In a novel approach, the copper II product can be rapidly converted backto a copper I compound using a reducing agent. Appropriate reducingagents for reducing copper II to copper I are known in the art. Usefulreducing agents for copper precursors include ethylene diamine,tetramethylethylenediamine, 3 aminopropanol, mono, di andtriethanolamine. Useful reducing agents are described in U.S. Pat. No.5,378,508, which is incorporated herein by reference in its entirety.The resulting copper I compound reacts further via disproportionation toform more copper and copper II compound. Through this approach withexcess reducing agent, copper I compounds can be used to form purecopper metal without any copper II compounds.

The copper compounds can also be used as capping agents to cap copperparticles. The copper particles can be nanoparticles. U.S. Pat.6,294,401 by Jacobsen describes capping procedures and is incorporatedherein in its entirety by reference.

As is discussed above, two or more molecular metal precursors can becombined in the precursor composition to form metal alloys and/or metalcompounds. For example, preferred combinations of metal precursors toform alloys based on silver include: Ag-nitrate and Pd-nitrate;Ag-acetate and [Pd(NH₃)₄](OH)₂; Ag-trifluoroacetate and [Pd(NH₃)₄](OH)₂;and Ag-neodecanoate and Pd-neodecanoate. One particularly preferredcombination of molecular metal precursors is Ag-trifluoroacetate andPd-trifluoroacetate. Another preferred alloy is Ag/Cu.

To form alloys, the two (or more) molecular metal precursors should havesimilar decomposition temperatures to avoid the formation of one of themetal species before the other species. Preferably, the decompositiontemperatures of the different molecular metal precursors are within 50°C., more preferably within 25° C.

Some applications require the utilization of a transparent orsemi-transparent conductive feature. For example, indium tin oxide (ITO)is useful for the formation of transparent conductive features, such asfor use in display applications. Antimony tin oxide (ATO) is useful as acolor tunable oxide layer that finds use in electrochromic applications.

Such transparent conductive features can also be fabricated according tothe present invention. For ITO, useful molecular precursors for indiuminclude: In-nitrate; In-chloride; In-carboxylates such as In-acetate;In-propionates including fluoro, chloro or bromo derivatives thereof;beta diketonates such as In- acetylacetonate,In-hexafluoroacetylacetonate and In-trifluoroacetylacetonate; pyrazolylborohydrides such as In(pz)₃BH; In-alkoxides and In-fluoroalkoxides; andIn-amides. Mixed alkoxo In-carboxylates such as indium isopropoxideethylhexanoate are also useful.

Useful molecular precursors for tin in ITO or ATO include: Sn-halidessuch as Sn-tetrachloride; Sn-dichloride; Sn-carboxylates such asSn-acetate or Sn-ethylhexanoate; Sn-alkoxides such as Sn(O^(t)Bu)₄;Sn-hydroxycarboxylates such as Sn-glycolate; and beta diketonates suchas Sn-hexafluoroacetylacetonate.

Useful molecular precursors for antimony include: Sb-trichloride;antimony carboxylates such as Sb-acetate or Sb-neodecanoate; antimonyalkoxides such as Sb-methoxide, Sb-ethoxide, Sb-butoxide.

The low viscosity precursor compositions according to the presentinvention preferably also include a solvent capable of solubilizing themolecular metal precursor discussed above. The solvent can be waterthereby forming an aqueous-based precursor composition. Water is moreenvironmentally acceptable than organic solvents. However, water cannottypically be used for deposition of the precursor composition ontohydrophobic substrates, such as tetrafluoroethylene fluorocarbonsubstrates (e.g., TEFLON, E.I. duPont deNemours, Wilmington, Del.)without modification of the substrate or the aqueous composition.

The solvent can also include an organic solvent, by itself or inaddition to water. The selected solvent should be capable ofsolubilizing the selected molecular metal precursor to a high level. Alow solubility of the molecular metal precursor in the solvent leads tolow yields of the conductor, thin deposits and low conductivity. Theprecursor compositions of the present invention exploit combinations ofsolvents and precursors that advantageously provide high solubility ofthe molecular precursor while still allowing low temperature conversionof the precursor to the conductor.

According to one embodiment of the present invention, the solubility ofthe molecular metal precursor in the solvent is preferably at leastabout 20 weight percent metal precursor, more preferably at least 40weight percent metal precursor, even more preferably at least about 50weight percent-metal precursor and most preferably at least about 60weight percent metal precursor. Such high levels of metal precursor leadto increased metal yield and the ability to deposit features havingadequate thickness.

The solvents can be polar or non-polar. Solvents that are usefulaccording to the present invention include amines, amides, alcohols,water, ketones, unsaturated hydrocarbons, saturated hydrocarbons,mineral acids organic acids and bases, Preferred solvents includealcohols, amines, amides, water, ketone, ether, aldehydes and alkenes.Particularly preferred organic solvents according to the presentinvention include N,N,-dimethylacetamide (DMAc), diethyleneglycolbutylether (DEGBE), ethanolamine and N-methyl pyrrolidone.

In some cases, the solvent can be a high melting point solvent, such asone having a melting point of at least about 30° C. and not greater thanabout 100° C. In this embodiment, a heated ink-jet head can be used todeposit the precursor composition while in a flowable state whereby thesolvent solidifies upon contacting the substrate. Subsequent processingcan then remove the solvent by other means and then convert the materialto the final product, thereby retaining resolution. Preferred solventsaccording to this embodiment are waxes, high molecular weight fattyacids, alcohols, acetone, N-methyl-2-pyrrolidone, toluene,tetrahydrofuran and the like. Alternatively, the precursor compositionmay be a liquid at room temperature, wherein the substrate is kept at alower temperature below the freezing point of the composition.

The solvent can also be a low melting point solvent. A low melting pointis required when the precursor composition must remain as a liquid onthe substrate until dried. A preferred low melting point solventaccording to this embodiment is DMAc, which has a melting point of about−20° C.

In addition, the solvent can be a low vapor pressure solvent. A lowervapor pressure advantageously prolongs the work life of the compositionin cases where evaporation in the ink-jet head, syringe or other toolleads to problems such as clogging. A preferred solvent according tothis embodiment is terpineol. Other low vapor pressure solvents includediethylene glycol, ethylene glycol, hexylene glycol,N-methyl-2-pyrrolidone, and tri(ethylene glycol) dimethyl ether.

The solvent can also be a high vapor pressure solvent, such as onehaving a vapor pressure of at least about 1 kPa. A high vapor pressureallows rapid removal of the solvent by drying. High vapor pressuresolvents include acetone, tetrahydrofuran, toluene, xylene, ethanol,methanol, 2-butanone and water.

As is discussed above, a vehicle is,a flowable medium that facilitatesthe deposition of the precursor composition. In cases where the liquidserves only to carry particles and not to dissolve molecular species,the terminology of vehicle is often used for the liquid. However, inmany precursor compositions, the solvent can also be considered thevehicle. The metal, such as silver, can be bound to the vehicle, forexample, by synthesizing a silver derivative of terpineol thatsimultaneously acts as both a precursor to silver and as a vehicle. Thisimproves the metallic yield and reduces the porosity of the conductivefeature.

Examples of preferred vehicles are listed in Table 4. Particularlypreferred vehicles according to the present invention include alphaterpineol, toluene and ethylene glycol. TABLE 4 Organic Vehicles Usefulin Precursor Compositions Formula/Class Name Alcohols 2-Octanol Benzylalcohol 4-hydroxy-3methoxy benzaldehyde Isodeconol Butylcarbitol Terpenealcohol Alpha-terpineol Beta-terpineol Cineol Esters 2,2,4trimethylpentanediol-1,3 monoisobutyrate Butyl carbitol acetate Butyloxalate Dibutyl phthalate Dibutyl benzoate Butyl cellosolve acetateEthylene glycol diacetate Ethylene glycol diacetateN-methyl-2-pyrrolidone Amides N,N-dimethyl formamide N,N-dimethylacetamide Aromatics Xylenes Aromasol Substituted Nitrobenzene aromaticso-nitrotoluene Terpenes Alpha-pinene, beta-pinene, dipentene, dipenteneoxide Essential Oils Rosemary, lavender, fennel, sassafras, wintergreen,anise oils, camphor, turpentine

The low viscosity precursor compositions in accordance with the presentinvention can also include one or more polymers. The polymers can bethermoplastic polymers or thermoset polymers. Thermoplastic polymers arecharacterized by being fully polymerized. They do not take part in anyreactions to further polymerize or cross-link to form a final product.Typically, such thermoplastic polymers are melt-cast, injection moldedor dissolved in a solvent. Examples include polyimide films, ABSplastics, vinyl, acrylic, styrene polymers of medium or high molecularweight and the like.

The polymers can also be thermoset polymers, which are characterized bynot being fully polymerized or cured. The components that make upthermoset polymers must undergo further reactions to form fullypolymerized, cross-linked or dense final products. Thermoset polymerstend to be resistant to solvents, heat, moisture and light.

A typical thermoset polymer mixture initially includes a monomer, resinor low molecular weight polymer. These components require heat,hardeners, light or a combination of the three to fully polymerize.Hardeners are used to speed the polymerization reactions. Some thermosetpolymer systems are two part epoxies that are mixed at consumption orare mixed, stored and used as needed.

Specific examples of thermoset polymers include amine or amide-basedepoxies such as diethylenetriamine, polyglycoldianine andtriethylenetetramine. Other examples include imidazole, aromaticepoxies, brominated epoxies, thermoset PET, phenolic resins such asbisphenol-A, polymide, acrylics, urethanes and silicones. Hardeners caninclude isophoronediamine and meta-phenylenediamene.

The polymer can also be an ultraviolet or other light-curable polymer.The polymers in this category are typically UV and light-curablematerials that require photoinitiators to initiate the cure. Lightenergy is absorbed by the photoinitiators in the formulation causingthem to fragment into reactive species, which can polymerize orcross-link with other components in the formulation. In acrylate-basedadhesives, the reactive species formed in the initiation step are knownas free radicals. Another type of photoinitiator, a cationic salt, isused to polymerize epoxy functional resins generating an acid, whichreacts to create the cure. Examples of these polymers includecyanoacrylates such as z-cyanoacrylic acid methyl ester with aninitiator as well as typical epoxy resin with a cationic salt.

The polymers can also be conductive polymers such as intrinsicallyconductive polymers. Conductive polymers are disclosed, for example, inU.S. Pat. No. 4,959,430 by Jonas et al., which is incorporated herein byreference in its entirety. Other examples of intrinsically conductivepolymers are listed in Table 5 below. TABLE 5 Intrinsically ConductivePolymers Examples Class/Monomers Catalyst/Dopant PolyacetylenePoly[bis(benzylthio) acetylene] Phenyl vinyl sulfoxide Ti alkylidenePoly[bis(ethylthio)acetylene] Poly[bis(methylthio)acetylene]1,3,5,7-Cyclooctatetraene Polyaniline Fully reduced organic sulfonicacids such as: Half oxidized Dinonylnaphthalenedisulfonc acidDinonylnaphthaleneusulfonic acid Dodecylbenzenesulfonic acidPoly(anilinesulfonic acid) Self-doped state Polypyrrole Organic sulfonicacid Polythiophene Poly(thiophine-2.5-diyl)2,5-Dibromo-3-alkyl/arylthiophene Poly(3-alkylthiophene-2.5-diyl) alkyl= butyl, hexyl, octyl, alkyl = butyl, hexyl, octyl, decyl, decyl,dodecyl dodecyl aryl = phenyl Poly(styrenesulfonate)/poly-Dibromodithiophene (2,3-dihydrothieno-[3,4-b]-1,4- Terthiophene dioxin)Other substituted thiophenes Poly(1,4-phenylenevinylene) (PPV)p-Xylylenebis (tetrahydrothiopheniumchloride)) Poly(1,4-phenylenesulfide) Poly(fluroenyleneethynylene)

Other additives can be included in the low viscosity precursorcompositions in accordance with the present invention. Among these arereducing agents to prevent the undesirable oxidation of metal species.Reducing agents are materials that are oxidized, thereby causing thereduction of another substance. The reducing agent loses one or moreelectrons and is referred to as having been oxidized. For example,popper and nickel metal have a strong tendency to oxidize. Thecompositions including nickel or copper precursors according to thepresent invention should preferably include reducing agents as additivesto provide reaction conditions for the formation of the metal at thedesired temperature, rather than the metal oxide. Reducing agents areparticularly applicable when using molecular metal precursor compoundswhere the ligand is not reducing by itself. Examples of reducing agentsinclude amino alcohols. Alternatively, the precursor conversion processcan take place under reducing atmosphere, such as hydrogen or forminggas.

In some cases, the addition of a reducing agent results in the formationof the metal even under ambient conditions. The reducing agent can bepart of the precursor itself, for example in the case of certainligands. An example is Cu-formate where the precursor forms copper metaleven in ambient air at low temperatures. In addition, the Cu-formateprecursor is highly soluble in water, results in a relatively highmetallic yield and forms only gaseous byproducts, which are reducing innature and protect the in-situ formed copper from oxidation. Copperformate is therefore a preferred copper precursor for aqueous basedprecursor compositions. Other examples of molecular metal precursorscontaining a ligand that is a reducing agent are Ni-acetylacetonate andNi-formate.

The precursor compositions can also include crystallization inhibitorsand a preferred crystallization inhibitor is lactic acid. Suchinhibitors reduce the formation of large crystallites directly from themolecular metal precursor, which can be detrimental to conductivity.Other crystallization inhibitors include ethylcellulose and polymerssuch as styrene allyl alcohol (SAA) and polyvinyl pirolydone (PVP). Forexample, in some silver precursor compositions small additions of lacticacid completely prevent crystallization. In other cases, such as inaqueous Cu-formate compositions, small amounts of glycerol can act as acrystallization inhibitor. Other compounds useful for reducingcrystallization are other polyalcohols such as malto dextrin, sodiumcarboxymethylcellulose and TRITON X100. In general, solvents with ahigher melting point and lower vapor pressure inhibit crystallization ofany given compound more than a lower melting point solvent with a highervapor pressure. In one embodiment, not greater than about 10 weightpercent crystallization inhibitor as a percentage of total compositionis added, preferably not greater than 5 weight percent and morepreferably not greater than 2 weight percent.

The low viscosity precursor compositions can also include an adhesionpromoter adapted to improve the adhesion of the conductive feature tothe underlying substrate. For example, polyamic acid can improve theadhesion of the composition to a polymer substrate. In addition, theprecursor compositions can include rheology modifiers. As an example,styrene allyl alcohol (SAA) can be added to the precursor composition toreduce spreading on the substrate.

The low viscosity precursor compositions can also include complexingagents. Complexing agents are a molecule or species that binds to ametal atom and isolates the metal atom from solution. Complexing agentsare adapted to increase the solubility of the molecular precursors inthe solvent, resulting in a higher yield of metal. One preferredcomplexing agent, particularly for use with Cu-formate and Ni-formate,is 3-amino-1-proponal. For example, a preferred precursor compositionfor the formation of copper includes Cu-formate dissolved in water and3-amino-1-propanol.

The low viscosity precursor compositions above can also include rheologymodifiers. Rheology modifiers can include SOLTHIX 250 (Avecia Limited),SOLSPERSE 21000 (Avecia Limited), styrene allyl alcohol (SAA), ethylcellulose, carboxy methylcellulose, nitrocellulose, polyalkylenecarbonates, ethyl nitrocellulose, and the like. These additives canreduce spreading of the precursor composition after deposition, as isdiscussed in more detail below.

The precursor compositions above can also include other components suchas wetting angle modifiers, humectants and the like.

In accordance with the foregoing, the low viscosity precursorcompositions according to the present invention can include combinationsof particles (nanoparticles and/or micron-size particles), molecularmetal precursor compounds, solvents, vehicles, reducing agents,crystallization inhibitors, adhesion promoters, and other minoradditives to control properties such as surface tension.

For low viscosity precursor compositions, it is preferred that the totalloading of particulates (nanoparticles and micron-size particles) is notgreater than about 75 weight percent, such as from about 5 wt. % toabout 50 wt. %. Loading in excess of the preferred amount can lead tohigher viscosities and undesirable flow properties. It is particularlypreferred that the total loading of micron-size particles not exceedabout 50 weight percent and that the total loading of nanoparticles notexceed about 75 weight percent. Intone preferred embodiment, the lowviscosity precursor composition includes from about 5 to about 50 weightpercent nanoparticles and substantially no micron-size particles.

A preferred low viscosity precursor composition comprises at least onemolecular metal precursor where the precursor is highly soluble in theselected aqueous or organic solvent. Preferably, the precursorcomposition includes at least about 20 weight percent of molecular metalprecursor, such as from about 30 weight percent to about 60 weightpercent. It is particularly preferred that the molecular metal precursorbe added to the precursor composition up to the solubility limit of theprecursor compound in the solvent.

According to the present invention, the precursor composition iscarefully selected to reduce the conversion temperature required toconvert the metal precursor compound to the conductive metal. Theprecursor converts at a low temperature by itself or in combination withother precursors and provides for a high metal yield. As used herein,the conversion temperature is the temperature at which the metal speciescontained in the molecular metal precursor compound, is at least 95percent converted to the pure metal. As used herein, the conversiontemperature is measured using a thermogravimetric analysis (TGA)technique wherein a 50-milligram sample of the precursor composition isheated at a rate of 10° C./minute in air and the weight loss ismeasured.

A preferred approach for reducing the conversion temperature accordingto the present invention is to bring the molecular metal precursorcompound into contact with a conversion reaction inducing agent. As usedherein, a conversion reaction inducing agent is a chemical compound thateffectively reduces the temperature at which the molecular metalprecursor compound decomposes to the metal. The conversion reactioninducing agent can either be added into the original precursorcomposition or added in a separate step during conversion on thesubstrate. The former method is preferred. Preferably, the conversiontemperature of the metal precursors can be preferably lowered by atleast about 25° C., more preferably by at least about 50° C. even morepreferably by at least about 100C., as compared to the dry metalprecursor compound.

The reaction inducing agent can be the solvent or vehicle that is usedfor the precursor composition. For example, the addition of certainalcohols can reduce the conversion temperature of the precursorcomposition. Preferred alcohols for use as, conversion reaction inducingagents according to the present invention include terpineol anddiethyleneglycol butylether (DEGBE). It will be appreciated that thealcohol can also be the vehicle, such as in the case of terpineol.

More generally, organic alcohols such as primary and secondary alcoholsthat can be oxidized to aldehydes or ketones, respectively, canadvantageously be used as the conversion reaction inducing agent.Examples are 1-butanol, diethyleneglycol, DEGBE, octanol, and the like.The choice of the alcohol is determined by its reducing capability aswell as its boiling point, viscosity and precursor solubilizingcapability. It has been discovered that some tertiary alcohols can alsolower the conversion temperature of some molecular precursors. Forexample, alpha-terpineol, which also serves as a vehicle, significantlylowers the conversion temperature of some molecular metal precursors.The boiling point of the conversion reaction inducing agents ispreferably high enough to provide for the preferred ratio of metal ionsto inducing agent during conversion to metal. It should also be lowenough for the inducing agent to escape the deposit cleanly withoutunwanted side reactions that could lead to carbon residues in the finalfilm. The preferred ratio of metal precursor to inducing agent isstoichiometric for complete reduction. However, in some cases catalyticamounts of the inducing agent are sufficient.

Some solvents, such as DMAc, can serve as a solvent, vehicle and aconversion reaction inducing agent. It can also be regarded as acomplexing agent for silver. This means that precursors such asAg-nitrate that are otherwise not very soluble in organic solvents canbe brought into solution by complexing the metal ion with a complexingagent such as DMAc. In this specific case, Ag-nitrate can form a 1:1adduct with DMAc which is soluble in organic solvents such asN-methylpyrrolidinone (NMP) or DMAc.

Another preferred approach to reducing the conversion temperature of themolecular precursor is utilizing a palladium compound as a conversionreaction inducing agent. According to this embodiment, a palladiumprecursor compound is added to the precursor composition, which includesanother precursor such as a silver precursor. With addition of variousPd compounds, the conversion temperature of the silver precursor can beadvantageously reduced by at least 25° C. and more preferably by atleast 50° C. Preferred palladium precursors according to this embodimentof the present invention include Pd-acetate, Pd-trifluoroacetate,Pd-neodecanoate and tetraammine palladium hydroxide. Pd-acetate andPd-trifluoroacetate are particularly preferred as conversion reactioninducing agents to reduce the conversion temperature of a silver metalcarboxylate compound. Small additions of Pd-acetate to a precursorcomposition that includes Ag-trifluoroacetate in DMAc can lower thedecomposition temperature by up to 80° C. Preferred are additions ofPd-acetate or Pd-trifluoracetate in an amount of at least about 1 weightpercent, more preferably at least about 2 weight percent. The upperrange for this Pd conversion reaction inducing agent is limited by itssolubility in the solvent and in one embodiment does not exceed about 10weight percent. Most preferred is the use of Pd-trifluoroacetate becauseof its high solubility in organic solvents. For example, a preferredprecursor composition for a silver/palladium alloy according to thepresent invention is Ag-trifluoroacetate and Pd-trifluoracetatedissolved in DMAc and lactic acid.

A complete range of homogenous Ag/Pd alloys can be formed with aAg-trifluoroacetate/Pd-trifluoroacetate combination in a solvent such asDMAc. The molecular mixing of the metal precursors provides preferredconditions for the formation of virtually any Ag/Pd alloy at lowtemperature. The conversion temperature of the silver precursor whendissolved in DMAc is preferably reduced by at least 80° C. when combinedwith Pd-trifluoroacetate. Pure Pd-trifluoroacetate dissolved in DMAc canbe converted to pure palladium at a similar temperature.

Other conversion reaction inducing agents that can also lower theconversion temperature for base metals such as nickel and copper can beused such as amines (ammonia, ethylamine, propylamine), amides (DMAc,dimethylformamide, methylformamide, imidazole, pyridine), alcohols suchas aminoalcohols (ethanol amine, diethanolamine and triethanolamine),aldehydes (formaldehyde, benzaldehyde, acetaldehyde); formic acid;thiols such as ethyl thioalcohol, phosphines such as trimethylphosphineor triethylphosphine and phosphides. Still other conversion reactioninducing agents can be selected from boranes and borohydrides such asborane-dimethylamine or borane-trimethylamine. Preferred conversionreaction inducing agents are alcohols and amides.

Another factor that has been found to influence the,conversiontemperature is the ratio of molecular metal precursor to conversionreaction inducing agent. It has been found that the addition of variousamounts of DEGBE to a molecular silver precursor such asAg-trifluoroacetate in DMAc further reduces the precursor conversiontemperature, for example by up to about 70° C. Most preferred is theaddition of stoichiometric amounts of the inducing agent such as DEGBE.Excess amounts of conversion temperature inducing agent are notpreferred because it does not lower the temperature any further. Inaddition, higher amounts of solvent or inducing agents lower the overallconcentration of molecular precursor in the precursor composition andcan negate other characteristics such as the composition being in thepreferred viscosity and surface tension range. The ratio of inducingagent to metal ion that is reduced to metal during conversion can beexpressed as a molar ratio of functional group (inducing part in thereducing agent) to metal ion. The ratio is preferably about 1, such asin the range from about 1.5 to about 0.5 and more preferably in therange of about 1.25 to about 0.75 for univalent metal ions such as Ag.For divalent metal ions the ratio is preferably about 2, such as in therange from about 3 to 1, and for trivalent metals the ratio ispreferably about 3, such as in the range from about 4.5 to 1.5.

The molecular precursor preferably provides as high a yield of metal aspossible. A preferred ratio of molecular precursor to solvent is thatcorresponding to greater than 10% mass fraction of metal relative to thetotal weight of the liquid (i.e., all precursor components excludingparticles). As an example, at least 10 grams of conductor is preferablycontained in 100 grams of the precursor composition. More preferably,greater than 20 wt. % of the precursor composition is metal, even morepreferably greater than 30 wt. %, even more preferably greater than 40wt. % and most preferably greater than 50 wt. %.

Yet another preferred approach for reducing the conversion temperatureis to catalyze the reactions using particles, particularlynanoparticles. Preferred powders that catalyze the reaction include purePd, Ag/Pd alloy particles and other alloys of Pd as well as Pt andalloys of Pt. Another approach for reducing the conversion temperatureis to use gaseous reducing agents such as hydrogen or forming gas.

Yet another preferred approach for reducing the conversion temperatureis ester elimination, either solvent assisted or without solvent assist.Solvent assist refers to a process wherein the metal alkoxide isconverted to an oxide by eliminating an ester. In one embodiment,a-metal carboxylate and metal alkoxide are mixed in the precursorcomposition. At the processing temperature the two precursors react andeliminate an organic ester to form a metal oxide, which decomposes tothe corresponding metal at a lower temperature than the precursorsthemselves. This is also useful for Ag and Au, where for Au the metaloxide formation is skipped.

Another preferred approach for reducing the conversion temperature is byphotochemical reduction. For example, photochemical reduction of Ag canbe achieved by using precursors containing silver bonds that can bebroken photochemically. Another method is to induce photochemicalreduction of a silver precursor on prepared surfaces where the surfacecatalyzes the photochemical reaction.

Another preferred approach for reducing the conversion temperature isin-situ precursor generation by reaction of ligands with particles. Forexample, silver oxide particles can be a starting material and can beincorporated into low viscosity precursor compositions in the form ofnanoparticles. The silver oxide can react with deprotonateable organiccompounds to form the corresponding silver salts. For example, silveroxide can be mixed with a carboxylic acid to form silver carboxylate.Preferred carboxylic acids include acetic acid, neodecanoic acid andtrifluoroacetic acid. Other carboxylic acids work as well. For example,DARVAN C (Vanderbilt Chemical) can react its carboxylic function withthe metal oxide. Small silver particles that are coated with a thinsilver oxide layer can also be reacted with these compounds. Anotherpotential benefit is simultaneously gained with regard to rheology inthat such a surface modification can lead to improved particle loadingsin low viscosity formulations. Another example is the reaction of CuOcoated silver powder with carboxylic acids. This procedure can beapplied more generally to other oxides such as copper oxide, palladiumoxide and nickel oxide particles as well. Other deprotonateablecompounds are halogeno-, hydroxy- and other alkyl and aryl derivativesof carboxylic acids, beta diketones, more acidic alcohols such asphenol, and hydrogentetrafluoroborates.

Thus, as is discussed above and illustrated by the examples below, theprecursor compositions of the present invention can have a precursorconversion temperature that is significantly lower than thedecomposition temperature of the dry metal precursor compound. In oneembodiment, the conversion temperature is not greater than about 250°C., such as not greater than about 225° C., more preferably is notgreater than about 200° C. and even more preferably is not greater thanabout 185° C. In certain embodiments, the conversion temperature can benot greater than about 150° C., such as not greater than about 125° C.and even not greater than about 100° C.

Substrates

The precursor compositions according to the present invention can bedeposited and converted to the conductive feature at low temperatures,thereby enabling the use of a variety of substrates having a relativelylow melting or decomposition temperature. During conversion of lowviscosity precursor compositions to the conductive feature, thesubstrate surface that the composition is printed onto significantlyinfluences how the overall conversion to a final structure occurs.

The types of substrates that are particularly useful according to thepresent invention include polyfluorinated compounds, polyimides, epoxies(including glass-filled epoxy), polycarbonates and many other polymers.Particularly useful substrates include cellulose-based materials such aswood or paper, acetate, polyester, polyethylene, polypropylene,polyvinyl chloride, acrylonitrile, butadiene (ABS), flexible fiberboard, non-woven polymeric fabric, cloth, metallic foil and thin glass.The substrate can be coated, for example a dielectric on a metallicfoil. Although the present invention can be used for suchlow-temperature substrates, it will be appreciated that traditionalsubstrates such as ceramic substrates can also be used in accordancewith the present invention.

According to a particularly preferred embodiment of the presentinvention, the substrate onto which the precursor composition isdeposited and converted to a conductive feature has a softening point ofnot greater than about 225° C., preferably not greater than about 200°C., even more preferably not greater than about 185° C. even morepreferably not greater than about 150° C. and even more preferably notgreater than about 100° C.

Deposition of Fine Features

One difficulty in printing and processing low viscosity precursorcompositions is that the composition can wet the surface and rapidlyspread to increase the width of the deposit, thereby negating theadvantages of fine line printing. This is particularly true when ink-jetprinting is employed to deposit fine features such as interconnects,because ink-jet technology puts strict upper boundaries on the viscosityof the composition that can be employed. Nonetheless, ink-jet printingis a preferred low-cost, large-area deposition technology that can beused to deposit the precursor compositions of the present invention.

According to a preferred embodiment of the present invention, the lowviscosity precursor compositions can be confined on the substrate,thereby enabling the formation of features having a small minimumfeature size, the minimum feature size being the smallest dimension inthe x-y axis, such as the width of a conductive line. The precursorcomposition can be confined to regions having a width of not greaterthan 100 μm, preferably not greater than 75 μm, more preferably notgreater than 50 μm, even more preferably not greater than 25 μm, andeven more preferably not greater than 10 μm, such as not greater thanabout 5 μm. The present invention provides compositions and methods ofprocessing that advantageously reduce the spreading of the low viscositycomposition. For example, small amounts of rheology modifiers such asstyrene allyl alcohol (SAA) and other polymers can be added to theprecursor composition to reduce spreading. The spreading can also becontrolled through combinations of nanoparticles and precursors.Spreading can also be controlled by rapidly drying the compositionsduring printing by irradiating the composition during deposition.

Spreading can also be controlled by the addition of a low decompositiontemperature polymer in monomer form. The monomer can be cured duringdeposition by thermal or ultraviolet means, providing a networkstructure to maintain line shape. The polymer can then be eitherretained or removed during subsequent processing of the conductor.

A preferred method is to pattern an otherwise non-wetting substrate withwetting enhancement agents that control the spreading and also yieldincreased adhesion. For example, this can be achieved by functionalizingthe substrate surface with hydroxide or carboxylate groups.

Fabrication of conductor features with feature widths of not greaterthan 100 μm or features with minimum feature size of not greater than100 μm from a low viscosity composition requires the confinement of thelow viscosity precursor compositions so that the composition does notspread over certain defined boundaries. Various methods can be used toconfine the composition on a surface, including surface energypatterning by increasing or decreasing the hydrophobicity (surfaceenergy) of the surface in selected regions corresponding to where it isdesired to confine the precursor or eliminate the precursor. These canbe classified as physical barriers, electrostatic and magnetic barriers,surface energy differences, and process related methods such asincreasing the precursor viscosity to reduce spreading, for example byfreezing or drying the composition very rapidly once it strikes thesurface.

In physical barrier approaches, a confining structure is formed thatkeeps the precursor composition from spreading. These confiningstructures may be trenches and cavities of various shapes and depthsbelow a flat or curved surface which confine the flow of the precursorcomposition. Such trenches can be formed by chemical etching or byphotochemical means. The physical structure confining the precursor canalso be formed by mechanical means including embossing a pattern into asoftened surface or means of mechanical milling, grinding or scratchingfeatures. Trenches can also be formed thermally, for example by locallymelting a low melting point coating such as a wax coating.Alternatively, retaining barriers and patches can be deposited toconfine the flow of composition within a certain region. For example, aphotoresist layer can be spin coated on a polymer substrate.Photolithography can be used to form trenches and other patterns in thisphotoresist layer. These patterns can be used to retain precursor thatis deposited onto these preformed patterns. After drying, thephotolithographic mask may or may not be removed with the appropriatesolvents without removing the deposited metal. Retaining barriers canalso be deposited with direct write deposition approaches such asink-jet printing or any other direct writing approach, as disclosedherein.

For example, a polymer trench can be ink-jet printed onto a flatsubstrate by depositing two parallel lines with narrow parallel spacing.A precursor composition can be printed between the two polymer lines toconfine the composition. Another group of physical barriers includeprinted lines or features with a certain level of porosity that canretain a low viscosity composition by capillary forces. The confinementlayer may comprise particles applied by any of the techniques disclosedherein. The particles confine the precursor composition that isdeposited onto the particles to the spaces between the particles becauseof wetting of the particles by the precurs6r composition. In oneembodiment, the particles are surface modified to make them hydrophilicand the composition is hydrophilic with the substrate being hydrophobic.

In one particular example, carbon particles are deposited onto asubstrate with a 75 μm resolution using electrostatic laser printing. A.silver precursor composition can be subsequently applied to this printedpattern and the resolution is retained while the printed line has a bulkconductivity of 10 milli-ohm-cm after heating at 200° C.

Surface energy patterning can be classified by how the patterning isformed, namely by mechanical, thermal, chemical or photochemical means.In mechanical methods, the physical structure confining the precursorcomposition is formed by mechanical means including embossing a patterninto a softened surface, milling features, or building up features toconfine the composition. In thermal methods, heating of the substrate isused to change the surface energy of the surface, either across theentire surface or in selected locations, such as by using a laser orthermal print head. In chemical methods, the entire surface or portionsof the surface are chemically modified by reaction with some otherspecies. In one embodiment, the chemical reaction is driven by locallaser heating with either a continuous wave or pulsed laser. Inphotochemical methods, light from either a conventional source or from alaser is used to drive photochemical reactions that result in changes insurface energy.

The methods of confining precursor compositions disclosed herein caninvolve two steps in series—first the formation of a confining pattern,that may be a physical or chemical confinement method, and second, theapplication of a precursor composition to the desired confinement areas.

Electrostatic printing can be used to print high resolution patternsthat correspond to at least two levels of surface energies. In oneembodiment, the electrostatic printing is carried out on a hydrophobicsurface and a hydrophilic material is printed. The regions where noprinting occurs correspond to hydrophobic material. A hydrophobicprecursor composition can then be printed onto the hydrophobic regionsthereby confining the composition. Alternatively, a hydrophiliccomposition can be printed onto the hydrophilic electrostaticallyprinted regions. The width of the hydrophobic and hydrophilic regionscan be not greater than 100 μm, more preferably are not greater than 75μm, more preferably not greater than about 50 μm and even morepreferably not greater than about 25 μm.

The precursor composition confinement may be accomplished by applying aphotoresist and then laser patterning the photoresist and removingportions of the photoresist. The confinement may be accomplished by apolymeric resist that has been applied by another jetting technique orby any other technique resulting in a patterned polymer. In oneembodiment, the polymeric resist is hydrophobic and the substratesurface is hydrophilic. In that case, the precursor composition utilizedis hydrophilic resulting in confinement of the composition in theportions of the substrate not covered by the polymeric resist.

A laser can be used in various ways to modify the surface energy of asubstrate in a patterned manner. The laser can be used to removehydroxyl groups through local heating. These regions are converted tomore hydrophobic regions that can be used to confine a hydrophobic orhydrophillic precursor composition. The laser can be used to removeselectively a previously applied surface layer formed by chemicalreaction of the surface with a silanating agent.

In one embodiment, a surface is laser processed to increase thehydrophilicity in regions where the laser strikes the surface. Apolyimide substrate coated with a thin layer of hydrophobic material,such as a fluorinated polymer. A laser, such as a pulsed YAG, excimer orother UV or shorter wavelength pulsed laser, can be used to remove thehydrophobic surface layer exposing the hydrophilic layer underneath.Translating (e.g., on an x-y axis) the laser allows patterns ofhydrophilic material to be formed. Subsequent application of ahydrophilic precursor composition to the hydrophilic regions allowsconfinement of the composition. Alternatively, a hydrophobic precursorcomposition can be used and applied to the hydrophobic regions resultingin composition confinement.

In another embodiment of the present invention, a surface is laserprocessed to increase the hydrophobicity in regions where the laserstrikes the surface. A hydrophobic substrate such as a fluorinatedpolymer can be chemically modified to form a hydrophilic layer on itssurface. Suitable modifying chemicals include solutions of sodiumnaphthalenide. Suitable substrates include polytetrafluoroethylene andother fluorinated polymers. The dark hydrophilic material formed byexposing the polymer to the solution can be removed in selected regionsby using a laser. Continuous wave and pulsed lasers can be used.Hydrophilic precursor compositions, for example aqueous basedcompositions, can be applied to the remaining dark material.Alternatively, hydrophobic precursor compositions, such as those basedon solutions in non-polar solvents, can be applied to the regions wherethe dark material was removed leaving the hydrophobic materialunderneath. Ceramic surfaces can be hydroxylated by heating in moist airor otherwise exposing the surface to moisture. The hydroxylated surfacescan be silanated to create a monolayer of hydrophobic molecules. Thelaser can be used to selectively remove the hydrophobic surface layerexposing the hydrophilic material underneath. A hydrophobic patternedlayer can be formed directly by micro-contact printing using a stamp toapply a material that reacts with the surface to leave exposed ahydrophobic material such as alkyl chain. The precursor composition canbe applied directly to the hydrophilic regions or hydrophobic regionsusing a hydrophilic or hydrophobic precursor composition, respectively.

A surface with patterned regions of hydrophobic and hydrophilic regionscan be formed by micro-contact printing. In this approach, a stamp isused to apply a reagent to selected regions of a surface. This reagentcan form a self-assembled monolayer that provides a hydrophobic surface.The regions between the hydrophobic surface regions can be used toconfine a hydrophilic precursor composition.

Precursor composition modification can also be employed to confine thecomposition on the substrate. Such methods restrict spreading of thecompositions by methods other than substrate modification. A precursorcomposition including a binder can be used for surface confinement. Thebinder can be chosen such that it is a solid at room temperature, but isa liquid suitable for ink-jet deposition at higher temperatures. Thesecompositions are suitable for deposition through, for example, a heatedink-jet head. The precursor composition can also include metalparticles. The precursor composition that is frozen on the surface canprovide linear features having widths of not greater than 100 μm, morepreferably not greater than 75 μm and more preferably not greater than50 μm. The precursor composition can also include a molecular precursorthat is capable of forming a metal when heated or irradiated by light.The precursor composition can combine conductive particles and amolecular precursor.

Binders can also be used in the precursor compositions of the presentinvention to provide mechanical cohesion and limit spreading of thecomposition after deposition. In one preferred embodiment, the binder isa solid at room temperature. During ink-jet printing, the binder isheated and becomes flowable. The binder can be a polymer or in somecases can be a precursor. In one embodiment, the binder is a solid atroom temperature, when heated to greater than 50° C. the binder meltsand flows allowing for ease of transfer and good wetting of thesubstrate, then upon cooling to room temperature the binder becomessolid again maintaining the shape of the deposited pattern. The bindercan also react-in some instances. Preferred binders include waxes,styrene allyl alcohols, poly alkylene carbonates, polyvinyl acetals,cellulose based materials, tetradecanol, trimethylolpropane andtetramethylbenzene. The preferred binders have good solubility in thesolvent used in the precursor composition and should be processable inthe melt form. For example, styrene allyl alcohol is soluble indimethylacetimide, solid at room temperature and becomes fluid-like uponheating to 80° C.

The binder in many cases should depart out of the ink-jet printedfeature or decompose cleanly during thermal processing, leaving littleor no residuals after processing the precursor composition. Thedeparture or decomposition can include vaporization, sublimation,unzipping, partial polymer chain breaking, combustion, or other chemicalreactions induced by a reactant present on the substrate material, ordeposited on top of the material.

An example of a precursor as a binder is the use of Ag-trifluoroacetatewith DMAc. The DMAc will form adducts with the Ag-trifluoroacetate whichthen acts as a binder as well as the silver precursor.

Other methods for controlling the spreading during printing of a lowviscosity precursor composition according to the present inventioninclude the steps of depositing a composition onto a cooled substrate,freezing the composition as the droplets contact the substrate, removingat least the solvent without melting the composition, and converting theremaining components of the composition to an electronic material. Themelting point of the composition is preferably less than 25° C.Preferred solvents include higher molecular weight alcohols. It ispreferred to cool the substrate to less than 10° C.

The surface of a substrate can be pretreated with a reactant, in oneembodiment a reactant that does not contain a metal. This reactant canbe a reducing agent for a metal-containing precursor. The surface can becompletely coated or regions can be coated with any approach includingscreen printing, ink-jet printing, spin coating, dip coating, spraying,or any other approach. In a second step, a metal containing reactant isink-jet printed onto the surface. The metal containing precursor reactswith the co-reactant on; the surface to form metal. The reaction israpid enough to confine the spreading of the metal on the surface. Inone embodiment, the metal containing precursor comprise silver orcopper. The co-reactant, on the surface can comprise a reducing agentfor the metal. Alternatively, a reducing agent or reaction inducingagent can be printed locally prior to or following the deposition of themetal precursor composition. By performing both printing steps within ashort time frame and by ensuring that the co-reactant triggereddecomposition reaction occurs fast enough to avoid spreading of theprecursor composition, fine features can be deposited. All themetal-containing compounds and reducing agents discussed herein can beused in this approach.

Yet another method for controlling the spreading of a low viscosityprecursor composition during printing is provided. The method comprisesdepositing a precursor composition onto a substrate, simultaneouslyirradiating the deposited composition with light to limit the spreadingof the composition on the surface and converting the composition to aconductive feature. UV light can be used to photochemically decompose ametal precursor to a metal before spreading of the precursor compositionoccurs.

Yet another method for controlling the spreading during printingaccording to the present invention comprises the steps of depositing aprecursor composition onto a porous substrate, thereby limiting thespreading of the composition, and converting the composition to aconductive feature. In one embodiment, the porosity in the substrate iscreated by laser patterning. The porosity can be limited to the verysurface of the substrate.

Yet another method for controlling the spreading of a low viscosityprecursor composition according to the present invention includes thesteps of patterning the substrate to form regions with two distinctlevels of porosity where the porous regions form the pattern of adesired feature. The precursor composition can then be deposited, suchas by ink-jet printing, onto the regions defining the pattern therebyconfining the precursor composition to these regions, and converting thedeposited precursor composition to a conductive feature. Preferredsubstrates are polyimide, and epoxy laminates. In one embodiment thepatterning is carried out with a laser. In another embodiment thepatterning is carried out using photolithography. In another embodiment,capillary forces pull at least some portion of the composition into theporous substrate.

Spreading of the precursor composition is influenced by a number offactors. A drop of liquid placed onto a surface will either spread ornot depending on the surface tensions of the liquid, the surface tensionof the solid and the interfacial tension between the solid and theliquid. If the contact angle is greater than 90 degrees, the liquid isconsidered non-wetting and the liquid tends to bead or shrink away fromthe surface. For contact angles less than 90 degrees, the liquid canspread on the surface. For the liquid to completely wet, the contactangle must be zero. For spreading to occur, the surface tension of theliquid must be lower than the surface tension of the solid on which itresides.

In one embodiment, a precursor composition is applied, as by ink-jetdeposition, to an unpatterned substrate. Unpatterned refers to the factthat the surface energy (tension) of the substrate has not beenintentionally patterned for the sole purpose of confining thecomposition. It is to be understood that variations in surface energy(used synonymously herein with surface tension) of the substrateassociated with devices, interconnects, vias, resists and any otherfunctional features may already be present. For substrates with surfacetensions of less than 30, a hydrophilic precursor composition can bebased on water, glycerol, glycol, and other solvents or liquids havingsurface tensions of greater than 30 dynes/cm, more preferably greaterthan 40 dynes/cm and preferably greater than 50 dynes/cm and evengreater than 60 dynes/cm. For substrates with surface tensions of lessthan 40, the solvents should have surface tensions of greater than 40dynes/cm, preferably greater than 50 dynes/cm and even more preferablygreater than 60 dynes/cm. For substrates with surface tensions less than50, the surface tension of the precursor composition should be greaterthan 50 dynes/cm, preferably greater than 60 dynes/cm. Alternatively,the surface tension of the composition can be chosen to be 5, 10, 15,20, or 25 dynes/cm greater than that of the substrate. Continuous inkjet heads often require surface tensions of 40 to 50 dynes/cm.Bubble-jet ink jet heads often require surface tensions of 35 to 45dynes/cm. The previously described methods are particularly preferredfor these types of deposition approaches.

In another embodiment, a precursor composition is applied, as by ink-jetdeposition, to an unpatterned low surface energy (hydrophobic) surfacethat has been surface modified to provide a high surface energy(hydrophilic). The surface energy can be increased by hydroxylating thesurface by various means known to those skilled in the art includingexposing to oxidizing agents and water,-heating in moist air and thelike. The surface tension of the precursor composition can then bechosen to be 5; 10, 15, 20, or 25 dynes/cm- less-than that of thesubstrate. Piezo-jet ink jet heads operating with hot wax often requiresurface tensions of 25 to 30 dynes/cm. Piezo-jet ink jet heads operatingwith UV curable inks often require surface tensions of 25 to 30dynes/cm. Bubble-jet ink jet heads operating with UV curable inks oftenrequire surface tensions of 20 to 30 dynes/cm. Surface tensions ofroughly . 20 to 30 dynes/cm are required for piezo-based ink jet headsusing solvents. The previously described methods are particularlypreferred for these types of applications.

Most electronic substrates with practical applications have low valuesof surface tension, in the range of 18 (polytetrafluroethylene) to 45,often between 20 and 40 dynes/cm. In one approach to confining aprecursor composition to a narrow line or other shape, a hydrophilicpattern corresponding to the pattern of the desired conductor feature isformed on the surface of a substrate through the methods discussedherein. A particularly preferred method uses a laser. For example, alaser can be used to remove a hydrophobic surface layer exposing ahydrophilic layer underneath. In one embodiment, the hydrophilicmaterial pattern on the surface has a surface energy that is 5, 10, 15,20, 25 or 30 dynes/cm greater than the surrounding substrate. In oneembodiment, the surface tension of the composition is chosen to be lessthan the surface tension of the hydrophilic region but greater than thesurface tension of the hydrophobic region. The surface tension of thecomposition can be chosen to be 5, 10, 15, 20 or 25 dynes/cm less thanthat of the hydrophilic regions. The surface tension of the compositioncan be chosen to be 5, 10, 15, 20 or 25 dynes/cm greater than that ofthe hydrophobic regions. In another approach, the surface energy of thecomposition is higher than the surface energy of both the hydrophobicand hydrophilic regions. The surface tension of the composition can bechosen to be 5, 10, 15, 20 or 25 dynes/cm greater than that of thehydrophilic regions. The surface tension of the ink is chosen to be 5,10, 15, 20 or 25 dynes/cm less than that of the hydrophilic regions.This approach is preferred for aqueous-based precursor compositions andcompositions with high surface tensions in general. Continuous ink jetheads often require surface tensions of 40 to 50 dynes/cm. Bubble-jetink jet heads often require surface tensions of 35 to 45 dynes/cm. Thepreviously described methods are particularly preferred for these typesof applications that can handle compositions with high surface tensions.

In one embodiment of this latter approach, a hydrophilic composition isapplied, as by ink-jet deposition, to the hydrophilic regions. Forsubstrates with unpatterned . hydrophobic regions with surface tensionsof less than 30, the hydrophilic composition can be based on water,glycerol, glycol, and other solvents or liquids to provide compositionshaving surface tensions of greater than 30 dynes/cm, more preferablygreater than 40, greater than 45, greater than 50, and even greater than60 dynes/cm. For substrates with surface tensions of less than 40 in thehydrophobic regions, the compositions should have surface tensions ofgreater than 40, greater than 45, greater than 50 and greater than 60dynes/cm. For substrates with surface tensions less than 50, the surfacetension of the composition should be greater than 50 greater than 55, orgreater than 60 dynes/cm. For hydrophilic regions with surface tensionsof less than 30, the hydrophilic precursor compositions can be based onwater, glycerol, glycol, and other solvents or liquids having surfacetensions of greater than 30 dynes/cm, greater than 35 dynes/cm, greaterthan 40 and greater than 50, and even greater than 60 dynes/cm. Forhydrophilic regions with surface tensions of less than 40, thecompositions should have surface tensions of greater than 40, greaterthan 50 and greater than 60 dynes/cm. For hydrophilic regions withsurface tensions less than 50, the surface tension of the compositionshould be greater than 50 or greater than 60 dynes/cm. For continuousink-jet heads that require surface tensions of 40 to 50 dynes/cm. Forbubble-jet ink-jet heads that require surface tensions of 35 to 45dynes/cm. The previously described methods are particularly preferredfor these types of applications.

In another approach to confining a composition to a narrow feature, ahydrophilic surface, or a hydrophobic surface that is renderedhydrophilic by surface modification, is patterned with a hydrophobicpattern. In one embodiment, the hydrophobic pattern has a surface energythat is 5, 10, 15, 20, 25 or 30 dynes/cm less than the surroundingsubstrate. This can be done by removing a hydrophilic surface layerusing a laser to expose a hydrophobic region underneath. A hydrophobicprecursor composition is applied to the hydrophobic surface regions toconfine the composition. In one embodiment, the hydrophobic compositionhas a surface energy that is 5, 10, 15, 20, 25 or 30 dynes/cm less thanthe surrounding substrate. In one embodiment, the hydrophobiccomposition has a surface energy that is 5, 10, 15, 20, 25 or 30dynes/cm greater than the surrounding substrate. In one embodiment, thehydrophobic precursor composition has a surface energy that is 5, 10,15, 20, 25 or 30 dynes/cm less than the hydrophobic surface pattern. Inone embodiment, the hydrophobic ink has;a surface energy that is 5, 10,15, 20, 25 or .30 dynes/cm greater than the hydrophobic surface pattern.In another embodiment, the surface tension of the composition is lessthan the hydrophilic regions and greater than the hydrophobic regions.The hydrophilic surface can have a surface tension of greater than 40,greater than 50 or greater than 60 dynes/cm. When the hydrophobicsurface has a surface energy of greater than 40 dynes/cm, it ispreferred to use an ink with surface tension of less than 40, even lessthan 30 dynes/cm, and less than 25 dynes/cm. When the hydrophobicsurface has a surface energy of greater than 50 dynes/cm, it ispreferred to use a composition with a surface tension of less than 50,preferably less than 40, even less than 30 dynes/cm, and more preferablyless than 25 dynes/cm. When the hydrophobic surface has a surfacetension of greater than 40 dynes/cm, it is preferred to use a precursorcomposition with a surface tension of less than 40, less than 35, lessthan 30 and even less than 25 dynes/cm.

Piezo-jet ink jet heads operating with hot wax often require surfacetensions of 25 to 30 dynes/cm. Piezo-jet ink jet heads operating with Uvcurable inks often require surface tensions of 25 to 30 dynes/cm.Bubble-jet ink jet heads operating with UV curable inks often requiresurface tensions of 20 -30 dynes/cm. Surface tensions of roughly 20 to30 dynes/cm are required for piezo-based ink jet heads using solvents.The previously described methods are particularly preferred for thesetypes of applications.

For ink-jet heads and other deposition techniques that require surfacetensions greater than 30 dynes/cm, a particularly preferred method forconfining a precursor composition to a surface involves increasing thehydrophilicity of the surface to provide a surface tension greater than40, greater than 45 or greater than 50 dynes/cm and then providing ahydrophobic surface pattern with surface tension lower than thesurrounding surface. The surface tension of the pattern can be 5, 10,15, 20 or 25 dynes/cm greater than the surface tension of thesurrounding substrate.

Surfactants, molecules with hydrophobic tails corresponding to lowersurface tension and hydrophilic ends corresponding to higher surfacetension can be use to modify the compositions and substrates to achievethe values of surface tensions and interfacial energies required.

For the purposes of this application, hydrophobic means a material thathas the opposite response to interaction with water. Hydrophobicmaterials have low surface tensions. They also do not have functionalgroups for making hydrogen bonds with water.

Hydrophilic means a material that has an affinity for water. Hydrophilicsurfaces are wetted by water. Hydrophilic materials also have highvalues of surface tension. They can also form hydrogen bonds with water.The surface tensions for different liquids are listed in Table 6 and thesurface energies for different solids are listed in Table 7. TABLE 6Surface Tensions of Various Liquids Surface Temp Tension Liquid (° C.)(dynes/cm) Water 20 72.75 Acetamide 85 C. 39.3 Acetone 20 C. 23.7Acetonitrile 20 29.3 n-butyl 20 C. 24.6 alcohol ethyl alcohol 20 24Hexane 20 18.4 Isopropyl 20 22 alcohol Glycerol 20 63.4 Glycol 20 47.7Tolulene 20 29

TABLE 7 Surface Energies of Various Solids Surface Energy Material(dynes/cm) Glass 30 PTFE 18 Polyethylene 31 Polyvinychlorides 41Polyvinylidene 25 fluoride Polypropylene 29 Polystyrene 33Polyvinylchloride 39 Polysulfone 41 Polycarbonate 42 Polyethylene 43terephthalate Polyacryonitrile 44 Cellulose 44

Another difficulty during printing and processing is that during drying,precursors in the composition can crystallize and form discontinuouslines that provide poor conductivity upon conversion to the conductor.This can be substantially prevented by adding small amounts of acrystallization inhibitor, as is discussed above.

The present invention also provides compositions and methods to increaseadhesion of the conductive feature, referred to herein as adhesionpromoters. Various substrates have different surface characteristicsthat result in varying degrees of adhesion. According to the presentinvention, the surface can be modified by hydroxylating or otherwisefunctionalizing the surface to provide reaction sites from the precursorcompositions. In one embodiment, the surface of a polyfluorinatedmaterial is modified by a sodium naphthalenide solution that providesreactive sites for bonding during reaction with the precursor. Inanother embodiment, a thin layer of metal is sputtered onto the surfaceto provide for better adhesion of precursor composition or conductivefeature to the substrate. In another embodiment, polyamic acid orsimilar materials are added to the composition that then bond with boththe conductor and surface to provide adhesion. Preferred amounts ofpolyamic acid and related compounds are from about 1 to 10 weightpercent of the low viscosity precursor composition.

In accordance with the foregoing, the precursor compositions accordingto the present invention can include a molecular precursor and avehicle, without nanoparticles or micron-size particles. In onepreferred embodiment, the precursor compositions include a conversionreaction inducing agent, which can be either or both of a powder, amolecular precursor or another inorganic or organic compound. In anotherembodiment, the low viscosity precursor composition includes additivesto reduce spreading of the composition by controlling the wetting angleof the composition on the surface. In another embodiment, thecombination of molecular precursor and solvent is chosen to provide ahigh solubility of the precursor in the solvent.

In another embodiment, the precursor composition includes hollow orporous micron-size particles, a molecular precursor and a vehicle. Themolecular precursor is preferably a metal organic compound. In anotherembodiment, the precursor composition includes hollow or porousmicron-size particles, nanoparticles and a vehicle. In anotherembodiment, the precursor composition includes hollow or porousmicron-size particles, a molecular precursor, nanoparticles and avehicle. The precursor is preferably a metal organic compound.

The precursor composition can also include a molecular precursor, avehicle and nanoparticles. The nanoparticles can be selected fromsilver, copper and other metals, or can be non-conductive nanoparticlessuch as silica, copper oxide and aluminum oxide.

The precursor compositions can also include a molecular precursor, avehicle, and a polymer or polymer precursor, such as in cases whereadhesion to a polymeric substrate is desired. The precursor to a polymercan be poly (amic) acid. The polymer can be an epoxy, polyimide,phenolic resin, thermoset polyester, polyacrylate and the like. The lowviscosity precursor compositions can include a low curing polymer, suchas one that cures at not greater than 200° C., more preferably notgreater than 150° C.

The precursor compositions can also include carbon, a molecularprecursor and a vehicle. The compositions can include particulatecarbon, such as conductive carbon, e.g., graphitic carbon. One preferredcombination is conductive carbon with a molecular precursor to silvermetal.

The precursor compositions can also include conductive transparentparticles (e.g., ITO particles), a molecular precursor and a vehicle.The molecular precursors can include ITO precursors and metal precursorssuch as silver precursors.

The precursors compositions can also include a conductive polymer,molecular precursor and a vehicle. The polymer can be conductive forboth electrons and protons. Electrically conductive polymers can beselected from polyacetylene, polyaniline, polyphenylene, polypyrrole,polythiophene, polyethylenedioxythiophene and poly (paraphenylenevinylene). Protonic conductive polymers include those with sulfonates orphosphates, for example sulfonated polyaniline.

The precursor compositions can also include glass or metal oxidenanoparticles, micron-size particles and a molecular precursor. Thecompositions can include nanoparticles of metal oxides such as silica,copper oxide, and aluminum oxide. Preferred molecular precursorsaccording to this embodiment are metal organics.

The precursor compositions can also include conductive nanoparticles andvehicle. The flowable composition can further include a polymerprecursor.

The low viscosity precursor compositions can also include anelectrocatalyst or catalyst and a precursor. The precursor can beconverted to a catalytically active material or can serve to fuse thelayer together.

In the low viscosity precursor compositions that include a molecularprecursor and powders (nanoparticles and/or micron-size particles), theratio of precursors to powders is close to that corresponding to theamount needed to fill the spaces between particulates with materialderived from the precursors. However, a significant improvement inconductivity can also be obtained for lower levels of molecularprecursor. When particles are included in the precursor compositions ofthe present invention, it is preferred that at least about 10 vol. %,more preferably at least about 25 vol. % and even more preferably atleast about 50 vol. % of the final conductor be derived from precursor.

Other specific low viscosity precursor compositions according to thepresent invention are preferred for different applications. Typically,the formulation for the low viscosity composition will take into accountthe deposition mechanism, the desired performance of the features andthe relative cost of the features. For example, simple circuitry on apaper substrate designed for a disposable, high-volume application willrequire a low cost precursor composition but will not require electronicfeatures having superior properties. On the other hand, higher endapplications such as for repair of electronic circuitry will requireelectronic features having very good electrical properties and therelative cost of the low viscosity precursor composition will typicallynot be a significant factor.

According to one embodiment, the precursor composition can includeparticulates, including insulative particles such as SiO₂, particulatesthat are a precursor to a conductive phase such as silver oxide orsilver nitrate particles, Ag trifluoroacetate crystallites, conductivemicron-size particles and nanoparticles of the conductive phase, and aliquid phase made up of a vehicle and molecular metal precursorsdissolved therein. For low viscosity compositions, the particulatefraction of the composition preferably is not greater than 25 volumepercent of the total composition volume. The precursor fraction of thecomposition, both present in the form of precursor particles andmolecular precursor dissolved in the vehicle, is typically expressed asa weight percent of the total composition weight and can be up to about80 weight percent of the total composition weight.

In one embodiment, the low viscosity precursor composition includes upto about 20 volume percent carbon and from about 10 to about 15 weightpercent of a molecular precursor, with the balance being vehicle andother additives. In another embodiment, the low viscosity precursorcomposition includes up to about 15 volume percent carbon and up toabout 5 volume percent metal nanoparticles, with the balance beingvehicle and other additives.

According to another embodiment, the low viscosity precursor compositionincludes up to about 75 weight percent metal nanoparticles, such as from5 to 50 weight percent metal nanoparticles, and from about 10 to about50 weight percent of a molecular precursor, wherein the balance isvehicle and other additives.

According to another embodiment, the low viscosity precursor compositionincludes up to about 20 volume percent micron-size metal particles andfrom about 10 to about 15 weight percent of a molecular precursor withthe balance being vehicle and other additives. After heating at notgreater than 250° C., the conductivity of the conductive feature is inthe range from 1 to 5 times the bulk metal conductivity.

According to yet another embodiment, the low viscosity precursorcomposition includes up to about 20 volume percent micron-size metalparticles, with the balance being a vehicle containing a precursor to aconductive polymer. After heating at not greater than 200° C. the bulkconductivity is in the range from 5 to 50 times the bulk conductivity ofthe metal phase.

In one embodiment of a transparent conductor precursor composition, thecomposition contains about 15 vol. % micron-size particles selected fromthe group of ITO, ATO, ZnO, SnO₂, and 5 vol. % Ag nanoparticles, andbetween 0 and 20 weight percent molecular precursor to Ag with thebalance being solvents, vehicle and other additives.

In another embodiment of a transparent conductor precursor formulation,the composition contains up to about 30 vol. % micron-size particlesselected from the group of ITO, ATO, ZnO, SnO₂, and between 5 and 40weight percent precursor to Ag, with the balance being solvents, vehicleand other additives.

In yet another embodiment, a transparent conductor precursor compositioncontains up to about 15 vol. % micron size particles selected from thegroup of ITO, ATO, ZnO, SnO₂, and up to 10 vol. % conductive glassparticles such as silver phosphate glass, and between 0 and 20 weightpercent precursor to Ag with the balance being solvents, vehicle andother additives.

In addition to the foregoing, the low viscosity precursor compositionsaccording to the present invention can also include carbon particles,such as graphitic particles. Depending upon the other components in thelow viscosity precursor composition, carbon particle loading up to about20 volume percent can be obtained in the compositions. The averageparticle size of the carbon particles is preferably not greater thanabout 1 μm and the carbon particles can advantageously have a bimodal ortrimodal particle size distribution. Graphitic carbon has a bulkresistivity of about 1375 μΩ-cm and is particularly useful in lowviscosity precursor compositions for conductive features that require arelatively low cost.

Deposition of Precursor Compositions

The low viscosity precursor compositions of the present invention can bedeposited onto surfaces using a variety of tools.

As used herein, a low viscosity deposition tool is a device thatdeposits a liquid or liquid suspension onto a surface by ejecting thecomposition through an orifice toward the surface without the tool beingin direct contact with the surface. The low viscosity deposition tool ispreferably controllable over an x-y grid, referred to herein as adirect-write deposition tool. A preferred direct-write deposition toolaccording to the present invention is an ink-jet device. Other examplesof direct-write deposition tools include aerosol jets and automatedsyringes, such as the MICROPEN tool, available from Ohmcraft, Inc., ofHoneoye Falls, N.Y.

For use in an ink-jet, the viscosity of the precursor compostion ispreferably not greater than 50 centipoise, such as in the range of fromabout 10 to about 40 centipoise. For use in an aerosol jet atomization,the viscosity is preferably not greater than about 20 centipoise.Automated syringes can use compositions having a higher viscosity, suchas up to about 5000 centipoise.

A preferred direct-write deposition tool according to the presentinvention is an ink-jet device. Ink-jet devices operate by generatingdroplets of the composition and directing the droplets toward a surface.The position of the ink-jet head is carefully controlled and can behighly automated so that discrete patterns of the composition can beapplied to the surface. Ink-jet printers are capable of printing at arate of 1000 drops per jet per second or higher and can print linearfeatures with good resolution at a rate of 10 cm/sec or more, up toabout 1000 cm/sec. Each drop generated by the ink-jet head includesapproximately 25 to 100 picoliters of the composition, which isdelivered to the surface. For these and other reasons, ink-jet devicesare a highly desirable means for depositing materials onto a surface.

Typically, an ink-jet device includes an ink-jet head with one or moreorifices having a diameter of not greater than about 100 μm, such asfrom about 50 μm to 75 μm. Droplets are generated and are directedthrough the orifice toward the surface being printed. Ink-jet printerstypically utilize a piezoelectric driven system to generate thedroplets, although other variations are also used. Ink-jet devices aredescribed in more detail in, for example, U.S. Pat. No. 4,627,875 byKobayashi et al. and U.S. Pat. No. 5,329,293 by Liker, each of which isincorporated herein by reference in their entirety. However, suchdevices have primarily been used to deposit inks of soluble dyes.

It is also important to simultaneously control the surface tension andthe viscosity of the precursor composition to enable the use ofindustrial ink-jet devices. Preferably the surface tension is from about10 to 50 dynes/cm, such as from about 20 to 40 dynes/cm, while theviscosity is maintained at not greater than about 50 centipoise.

According to one embodiment, the solids loading of particles in the lowviscosity precursor composition is preferably as high as possiblewithout adversely affecting the viscosity or other necessary propertiesof the composition. For example, the low viscosity precursor compositioncan have a particle loading of up to about 75 weight percent, and in oneembodiment the particle loading is from about 5 to about 50 weightpercent.

The precursor compositions for use in an ink-jet device can also includewater and an alcohol. Surfactants can also be used to maintain theparticles in suspension. Co-solvents, also known as humectants, can beused to prevent the precursor composition from crusting and clogging theorifice of the ink-jet head. Biocides can also be added to preventbacterial growth over time. Examples of such ink-jet liquid vehiclecompositions are; disclosed in U.S. Pat. No. 5,853,470 by Martin et al.;U.S. Pat. No. 5,679,724 by Sacripante et al.; U.S. Pat. No. 5,725,647 byCarlson et al.; U.S. Pat. No. 4,877,451 by Winnik et al.; U.S. Pat. No.5,837,045 by Johnson et al.; and U.S. Pat. No. 5,837,041 by Bean et al.Each of the foregoing U.S. patents is incorporated by reference hereinin their entirety. The selection of such additives is based upon thedesired properties of the composition, as is known to those skilled inthe art. Particles can be mixed with the liquid vehicle using a mill or,for example, an ultrasonic processor.

The low viscosity precursor compositions according to the presentinvention can also be deposited by aerosol jet deposition. Aerosol jetdeposition can enable the formation of conductive features having afeature width of not greater than about 200 μm, such as not greater than100 μm, not greater than 75 μm and even not greater than 50 μm. Inaersol jet deposition, the precursor composition is aerosolized intodroplets and the droplets are transported to the substrate in a flow gasthrough a flow channel. Typically, the flow channel is straight andrelatively short.

The aerosol can be created using a number of atomization techniques.Examples include ultrasonic atomization, two-fluid spray head, pressureatomizing nozzles and the like. Ultrasonic atomization is preferred forcompositions with low viscosities and low surface tension. Two-fluid andpressure atomizers are preferred for higher viscosity fluids. Solvent orother precursor components can be added to the precursor compositionduring atomization, if necessary, to keep the concentration of precursorcomponents substantially constant during atomization.

The size of the aerosol droplets can vary depending on the atomizationtechnique. In one embodiment, the average droplet size is not greaterthan about 10 μm and more preferably is not greater than about 5 μm.Large droplets can be optionally removed from the aerosol, such as bythe use of an impactor.

Low aerosol concentrations require large volumes of flow gas and can bedetrimental to the deposition of fine features. The concentration of theaerosol can optionally be increased, such as by using a virtualimpactor. The concentration of the aerosol can be greater than about 10⁶droplets/cm³ and more preferably is greater than 10⁷ droplets/cm³. Theconcentration of the aerosol can be monitored and the information can beused to maintain the mist concentration within, for example, 10% of thedesired mist concentration over a period of time.

The droplets are deposited onto the surface of the substrate by inertialimpaction of larger droplets, electrostatic deposition of chargeddroplets, diffusional deposition of sub- micron droplets, interceptiononto non-planar surfaces and settling of droplets, such as those havinga size in excess of about 10 μm.

Examples of tools and methods for the deposition of fluids using aerosoljet deposition include U.S. Pat. No. 6,251,488 by Miller et al., U.S.Pat. No. 5,725,672 by Schmitt et al. and U.S. Pat. No. 4,019,188 byHochberg et al. Each of these U.S. Patents is incorporated herein byreference in their entirety.

The precursor compositions of the present invention can also bedeposited by a variety of other techniques including intaglio, rollprinter, spraying, dip coating, spin coating, and other techniques thatdirect discrete units of fluid or continuous jets, or continuous sheetsof fluid to a surface. Other printing methods include lithographic andgravure printing.

For example, gravure printing can be used with precursor compositionshaving a viscosity of up to about 5000 centipoise. The gravure methodcan deposit features having an average thickness of from about 1 μm toabout 25 μm micrometers and can deposit such features at a high rate ofspeed, such as up to about 700 meters per minute. The gravure processalso enables the direct formation of patterns onto the surface.

Lithographic printing methods can also be utilized. In the lithographicprocess, the inked printing plate contacts and transfers a pattern to arubber blanket and the rubber blanket contacts and transfers the patternto the surface being printed. A plate cylinder first comes into contactwith dampening rollers that transfer an aqueous solution to thehydrophilic non-image areas of the plate. A dampened plate then contactsan inking roller and accepts the ink only in the oleophillic imageareas.

Using one or more of the foregoing deposition techniques, it is possibleto deposit the precursor composition on one side or both sides of asubstrate. Further, the processes can be repeated to deposit multiplelayers of the same or different precursor compositions on a substrate.

An optional first step, prior to deposition of the precursorcomposition, is surface modification of the substrate as is discussedabove. The surface modification can be applied X to the entire substrateor can be applied in the form of a pattern, such as by usingphotolithography. The surface modification can include increasing ordecreasing the hydrophilicity of the substrate surface by chemicaltreatment. For example, a silanating agent can be used on the surface ofa glass substrate to increase the adhesion and/or to control spreadingof the precursor composition through modification of the surface tensionand/or wetting angle. The surface modification can also include the useof a laser to clean the substrate. The surface can also be subjected tomechanical modification by contacting with another type of surface. Thesubstrate can also be modified by corona treatment. For the depositionof organic-based precursor compositions, the activation energy of thesubstrate surface can be modified.

For example, a line of polyimide can be printed prior to deposition of aprecursor composition, such as a silver metal precursor composition, toprevent infiltration of the composition into a porous substrate, such aspaper. In another example, a primer material may be printed onto asubstrate to locally etch or chemically modify the substrate, therebyinhibiting the spreading of the precursor composition being deposited inthe following printing step. In yet another example, a via can be etchedby printing a dot of a chemical that is known to etch the substrate. Thevia can then be filled in a subsequent printing process to connectcircuits being printed on the front and back of the substrate.

As is discussed above, the deposition of the low viscosity precursorcomposition can be carried out by pen/syringe, continuous or drop ondemand ink-jet, droplet deposition, spraying, flexographic printing,lithographic printing, gravure printing, other intaglio printing, andothers. The precursor composition can also be deposited by dip-coatingor spin-coating, or by pen dispensing onto a rod or fiber typesubstrates with the same composition. Immediately after deposition, thecomposition may spread, draw in upon itself, or form patterns dependingon the surface modification discussed above. In another embodiment, amethod is provided for processing the deposited composition using 2 ormore jets or other ink sources: In one embodiment, the first depositionstep provides the precursor composition, including a molecular metalprecursor compound while the second deposition step provides a reducingagent or other co-reactant that converts the precursor and/or reducesthe conversion temperatures Another example of a method for processingthe deposited composition is using infiltration into a porous bed formedby a previous fabrication method. Another method for depositing thecomposition is using multi-pass deposition to build the thickness of thedeposit. Another example of a method for depositing the composition isusing a heated head to decrease the viscosity of the composition.

The properties of the deposited precursor composition can also besubsequently modified. This can include freezing, melting and otherwisemodifying the properties such as viscosity with or without chemicalreactions or removal of material from the precursor composition. Forexample, a low viscosity precursor composition including a UV-curablepolymer can be deposited and immediately exposed to an ultraviolet lampto polymerize and thicken and reduce spreading of the composition.Similarly, a thermoset polymer can be deposited and exposed to a heatlamp or other infrared light source. After deposition, the precursorcomposition is treated in one or more steps to convert the metalprecursor and obtain the desired final properties of the depositedfeature.

After deposition, the precursor composition is treated to convert theprecursor composition to the conductive feature. The treatment caninclude multiple steps, or can occur in a single step, such as when theprecursor composition is rapidly heated and held at the conversiontemperature for a sufficient amount of time to form the conductivefeature.

An optional, initial step can include drying or subliming of thecomposition by heating or irradiating. In this step, material is removedfrom the composition and/or chemical reactions occur in the composition.An example of a method for processing the deposited composition in thismanner is using a UV, IR, laser or a conventional light source. Heatingrates for drying the precursor composition are preferably greater thanabout 10° C./min, more preferably greater than 100° C./min and even morepreferably greater than 1000° C./min. The temperature of the depositedprecursor composition can be raised using hot gas or by contact with aheated substrate. This temperature increase may result in furtherevaporation of solvents and other species. A laser, such as an IR laser,can also be used for heating. IR lamps or a belt furnace can also beutilized. It may also be desirable to control the cooling rate of thedeposited feature.

After drying, the next step is to react the molecular metal precursors.In one embodiment, the precursor composition is reacted using variousgases to assist in the conversion of the precursor composition to aconductive feature. For example, hydrogen, nitrogen, and reducing gasescan be used to assist the reaction. Copper, nickel, and other metalsthat oxidize when exposed to oxygen may require the presence of reducingatmospheres. It has been found that the precursor compositions of thepresent invention can advantageously provide very short reaction timeswhen processed with light (e.g., a laser) that heats the materials. Thisis a result of the high chemical reaction rates when sufficiently hightemperatures are provided for a specific precursor and the ability oflight to rapidly heat the materials over time scales of milliseconds oreven less. In the case of precursor compositions including particles,phases having a low melting or softening point allow short processingtimes.

The precursor compositions of the present invention can be processed forvery short times and still provide useful materials. Short heating timescan advantageously prevent damage to the underlying substrate. Preferredthermal processing times for deposits having a thickness on the order ofabout 10 μm are not greater than about 100 milliseconds, more preferablynot greater than about 10 milliseconds, more preferably not greater thanabout 1 millisecond. The short heating times can be provided using laser(pulsed or continuous wave), lamps, or other radiation. Particularlypreferred are scanning lasers with controlled dwell times. Whenprocessing with belt and box furnaces or lamps, the hold time ispreferably not greater than 60 seconds, and more preferably not greaterthan 30 seconds, and even more preferably not greater than 10 seconds.The heating time can even be not greater than 1 second when processedwith these heat sources, and even not greater than 0.1 second whilestill providing conductive materials that are useful in a variety ofapplications. The preferred heating time and temperature will alsodepend on the nature of the electronic feature. It will be appreciatedthat short heating times may not be beneficial if the solvent or otherconstituents boil rapidly and form porosity or other defects in thefeature.

When used to form conductors the deposited precursor compositions can besubstantially fully converted at temperatures of not greater than 300°C., more preferably not greater than 250° C., more preferably notgreater than 225° C.; even more preferably not greater than 200° C., andeven more preferably not greater than 185° C.

The particles in the precursor composition (if any) or the materialderived from the precursor can optionally be sintered subsequent todecomposition of the metal precursor. The sintering can be carried outusing furnaces, light sources such as heat lamps and/or lasers. In oneembodiment, the use of a laser advantageously provides very shortsintering times and in one embodiment the sintering time is not greaterthan 1 second, more preferably not greater than 0.1 seconds and evenmore preferably not greater than 0.01 seconds. Laser types includepulsed and continuous wave. In one embodiment, the laser pulse length istailored to provide a depth of heating that is equal to the thickness ofthe material to be sintered. The components in the precursor compositioncan be fully or partially reacted before contact with laser light. Thecomponents can be reacted by exposure to the laser light and thensintered.

The conductive feature can be post-treated after deposition andconversion of the metal precursor. For example, the crystallinity of thephases present can be increased, such as by laser processing. Thepost-treatment can also include cleaning and/or encapsulation of theelectronic features, or other modifications.

It will be appreciated from the foregoing discussion that two or more ofthe latter process steps (drying, heating, reacting and sintering) canbe combined into a single process step.

One preferred process flow includes the steps of: forming a structure byconventional methods such as lithographic, gravure, flexo, screenprinting, photo patterning, thin film or wet subtractive approaches;identifying locations requiring addition of material; adding material bya direct deposition of a low viscosity composition; and processing toform the final product. In a specific embodiment, a circuit is preparedby screen-printing and is then repaired by localized printing of a lowviscosity precursor composition.

More specifically, the present invention provides a method for therepair of a feature by ink-jet printing or syringe dispensing. In oneembodiment, the method includes the steps of ink-jet printing aprecursor composition onto a repair region and heating to temperaturessufficient to convert the precursor composition to a substantially pureconductor. According to one embodiment of the present invention, therepair feature is a ball grid array (BGA). According to anotherembodiment, the feature is a circuit pattern in a low temperature cofireceramic (LTCC) layer. In one embodiment, the pattern is not yet sinteredwhile in another embodiment the pattern is already sintered. In oneembodiment, a laser can be used to heat the repair section, The repaircan be carried out prior to processing of the part. The repair can bemade to a metallic conductor or other electronic feature. The repairedportion can have been formed by screen-printing or photopatterning of aparticle-containing composition. In one embodiment, laser trimming isused to further define the repair region after ink-jet deposition.

According to one embodiment of the present invention, the repairedfeature preferably has a minimum feature size that is not greater thanabout 250 μm and more preferably is not greater than about 100 μm.According to one embodiment, the repaired feature has a minimum featuresize not greater than about 10 μm. The repair can be made to featuresderived from various processes such as chemical vapor deposition,evaporation, sputtering or other thin film techniques.

In another embodiment, features larger than approximately 100 μm arefirst prepared by screen-printing. Features not greater than about 100μm are then deposited by a direct deposition method using a lowviscosity precursor composition.

In yet another embodiment, a polyimide surface is first modified topromote adhesion of the low viscosity precursor composition. Theprecursor composition is deposited, and then is dried and converted at atemperature of not greater than 300° C. After deposition and conversion,the feature can then optionally be laser sintered.

Preferably, the conductive feature has a resistivity that is not greaterthan 10 times the bulk resistivity of the metal, preferably not greaterthan 6 times the bulk resistivity, more preferably not greater than 4times the bulk resistivity and most preferably not greater than 2 timesthe bulk resistivity of the metal.

According to the present invention, the low viscosity precursorcomposition can be deposited, dried, and reacted with a total reactiontime of not greater than about 100 seconds, more preferably not greaterthan about 10 seconds and even more preferably not greater than about 1second.

In yet another embodiment, the low viscosity precursor composition canbe deposited, dried, and reacted, wherein the total time for deposition,drying and reaction is not greater than about 1 minute, more preferablynot greater than about 10 seconds and even more preferably not greaterthan about 1 second.

The product compositions derived from the printed low viscosityprecursor compositions of the present invention can include a variety ofmaterial combinations.

In one embodiment, a conductive,feature comprises silver and copper. Ina preferred embodiment, the feature includes discrete regions of coppermetal that are derived from particles, preferably particles having anaverage size of not greater than 1 μm. According to this embodiment, thecopper metal is dispersed in a matrix of silver that is derived from amolecular metal precursor. The silver and copper are not substantiallyinterdiffused as when derived from high fire compositions. In oneembodiment, the feature includes about 85 vol. % copper and 15 vol. %silver. In another embodiment, the silver derived from the precursoralso includes an amount of copper, palladium, platinum or some othermetal that provides resistance to electromigration or powdersolderability.

In another embodiment, the conductive feature includes silver andpalladium. In a preferred embodiment, the feature includes regions ofsubstantially pure dispersed silver in a matrix of silver-palladium thatprovides resistance to solder leaching. In a particularly preferredembodiment, the silver-palladium is derived from precursors and theoverall feature includes not greater than about 2 vol. % palladium, morepreferably not greater than about 1 vol. % palladium. In anotherembodiment, the palladium is replaced with another metal derived from aprecursor to provide a silver matrix that includes an amount of copper,platinum or some other metal that provides resistance toelectromigration or solder leaching.

In yet another embodiment, the feature comprises silver or copperderived from a precursor and an insulating phase. The insulating phaseis preferably a glass or metal oxide. Preferred glasses are aluminumborosilicates, lead borosilicates and the like. Preferred metal oxidesare silica, titania, alumina, and other simple and complex metal oxides.The insulating phase can be derived from particles or precursors. Thisembodiment is particularly useful for the production of low ohmresistors.

In an embodiment preferred for transparent and conducting materials,zinc oxide, antimony tin oxide (ATO), indium tin oxide (ITO) andmixtures of these are contained in a feature. In a preferred embodiment,the feature comprises a small amount of metal to improve theconductivity while only slightly degrading conductivity by choosingprocessing conditions to provide metal regions not greater than about100 nanometers in size.

The conductor composition can also be a composite of dissimilarmaterials. The composite can include metal-metal oxide, metal-polymer,metal-glass, carbon-metal, and other combinations. The conductorcomposition can also include solder-like compositions. The compositioncan include silver, lead, tin, indium, copper, and other elements.

In accordance with the foregoing direct-write processes, the presentinvention enables the formation of features for devices and componentshaving a small minimum feature size. For example, the method of thepresent invention can be used to fabricate features having a minimumfeature size (the smallest feature dimension in the x-y axis) of notgreater than about 100 μm, more preferably not greater than about 75 μm,even more preferably not greater than 50 μm and even more preferably notgreater than 25 μm. The minimum feature size can even be not greaterthan about 10 μm and even not greater than about 5 μm. These featuresizes can be provided using ink-jet printing and other printingapproaches that provide droplets or discrete units of low viscositycomposition to a surface. The small feature sizes can advantageously beapplied to various components and devices, as is discussed below.

Conductor Properties and Structure

The conductors formed by the present invention have combinations ofvarious features that have not been attained using other low viscosityprecursors. The conductive features preferably have a high purity, ahigh electrical conductivity and high electromigration resistance. Highconductivity can be provided through the low viscosity compositionscomprising precursors to silver, platinum, palladium, gold, nickel orcopper.

The present invention is particularly useful for fabrication ofconductors with resistivities that are not greater than 20 times theresistivity of the substantially pure bulk conductor, more preferablynot greater than 10 times the substantially pure bulk conductor, evenmore preferably not greater than 6 times and most preferably not greaterthan 2 times that of the substantially pure bulk conductor.

However, it will be appreciated that the properties of the conductivefeature can vary depending upon the particular application. For example,it may be desirable for some applications to process the feature at avery low temperature where low resistivity is not a major factor.According to one embodiment, a precursor composition can be depositedand converted at a temperature of not greater than 125° C., where theresistivity of the feature is not greater than about 200 times theresistivity of the pure bulk conductor, more preferably not greater thanabout 100 times the resistivity of the bulk conductor and even morepreferably not greater than about 80 times the resistivity of the bulkconductor.

After heating, the compositions of the present invention will yieldsolids with specific bulk resistivity values. As a background, bulkresistivity values of a number of solids are provided in Table 8. TABLE8 Bulk Resistivity of Various Materials Bulk Resistvity Material(micro-Ω cm) silver (Ag − thick film material fired at 850° C.) 1.59copper (Cu) 1.68 gold (Au) 2.24 aluminum (Al) 2.64 Ferro CN33-246 (Ag +low melting glass, 2.7-3.2 fired at 150° C.) SMP Ag flake + precursorformulation, 250° C. 4.5 molybdenum (Mo) 5.2 Tungsten (W) 5.65 zinc (Zn)5.92 nickel (Ni) 6.84 iron (Fe) 9.71 palladium (Pd) 10.54 tin (Sn) 11solder (Pb—Sn; 50:50) 15 Lead 20.64 Titanium nitrate (TiN transparentconductor) 20 duPont Polymer Thick Film 5029 (state of the art Ag filledpolymer, 150° C.) 18-50 duPont Polymer Thick Film (Cu filled polymer) 75-300 ITO indium tin oxide (In₂O₃:Sn) 100 zinc oxide (ZnOdoped-undoped) 120-450 carbon (C-graphite) 1375 KIA SCC-10 (doped silverphosphate glass, 3000 330° C. soft point) ruthenium oxide RuO₂ typeconductive oxides   5000-10,000 Bayer conductive polymer Baytron-P1,000,000

According to one embodiment of the present invention, a low viscosityprecursor composition includes up to about 20 volume percent micron-sizemetal particles and from about 10 to about 15 weight percent of amolecular metal precursor with the balance being vehicle and otheradditives. After heating at between 200° C. and 300° C., the feature canhave a bulk conductivity in the range from 1 to 5 times the bulk metalconductivity.

According to another embodiment of the present invention, a lowviscosity precursor composition includes up to about 20 volume percentmicron-size metal particles, with the balance being a vehicle containinga precursor to a conductive polymer. After heating at between 100° C.and 200° C., the feature can have a bulk conductivity in the range from5 to 50 times the bulk conductivity of the metal phase.

According to another embodiment of the present invention, a transparentconductor ink formulation includes about 15 vol. % micron-size particlesselected from the group of ITO, ATO, ZnO, SnO₂, and 5 vol. % Agnanoparticles, and between 0 and 20 weight percent precursor to Ag withthe balance being solvents, vehicle and other additives. After firing atbetween 250° C. and 400° C. the feature can have a bulk conductivity inthe range from 500 to 1000 micro-ohm-centimeter.

A transparent conductor ink formulation includes up to about 30 vol. %micron-size particles selected from the group of ITO, ATO, ZnO, SnO₂,and between 5 and 40 weight percent precursor to Ag, with the balancebeing solvents, vehicle and other additives. After firing at between150° C. and 300° C., the feature can have a conductivity in the rangefrom 500 to 1000 micro-ohm-centimeter.

According to another embodiment of the present invention, a transparentconductor ink formulation includes up to about 15 vol. % micron-sizeparticles selected from the group of ITO, ATO, ZnO, SnO₂, and up to 10vol. % conductive glass particles such as silver phosphate glass, andbetween 0 and 20 weight percent precursor to Ag, with the balance beingsolvents, vehicle and other additives. After firing at between 300° C.and 500° C., the feature can have a bulk conductivity in the range from300 to 800 micro-ohm-centimeter.

According to another embodiment of the present invention, a low costconductor precursor composition includes between 5 and 20 vol. %micron-size particles selected from the group of amorphous carbon,carbon graphite, iron, nickel, tungsten, molybdenum, and between 0 and 5vol. % nanoparticles selected from the group of Ag; carbon,intrinsically conductive polymer, Fe, Cu, Mo, W, and between 0 and 20weight percent precursor to a metal such as Ag, with the balance beingsolvents, vehicle and other additives. After heating at between 250° C.and 400° C., the feature can have a bulk conductivity in the range from100 to 4000 micro-ohm-centimeter.

According to another embodiment of the present invention, a low costconductor precursor composition includes between 5 and 20 vol %micron-size particles selected from the group of amorphous carbon,graphite, iron, nickel, tungsten, molybdenum, and between 20 and 50weight percent precursor to an intrinsically conductive polymer, withthe balance being solvents, vehicle and other additives. After heatingat between 100° C. and 200° C., the feature can have a bulk conductivityin the range from 5,000 to 15,000 micro-ohm-centimeter.

The silver-palladium compositions of the present invention can alsoprovide resistance to solder leaching. In one embodiment, thecompositions provide resistance to 3 dips in standard 60/40 lead-tinsolder at its melting point.

The compositions and methods of the present invention advantageouslyallow the fabrication of various unique structures.

In one embodiment, the average thickness of the deposited feature isgreater than about 0.01 μm, more preferably is greater than about 0.05μm, even more preferably is greater than about 0.1 μm and even morepreferably is greater than about 0.5 μm. The thickness can even begreater than about 1 μm, such as greater than about 5 μm. Thesethicknesses can be obtained by ink-jet deposition or deposition ofdiscrete units of material by depositing more than a single layer. Asingle layer can be deposited and dried, followed by repetitions of thiscycle.

Vias can also be filled with the low viscosity precursor compositions ofthe present invention. The via can be filled, dried to remove the volumeof the solvent, filled further and two or more cycles of this type canbe used to fill the via. The via can then be processed to convert thematerial to its final composition. After conversion, it is also possibleto add more precursor composition, dry and then convert the material toproduct to replace the volume of material lost upon conversion to thefinal product.

The compositions and methods of the present invention can also be usedto form dots, squares and other isolated regions of material. Theregions can have a minimum feature size of not greater than 250 μm, suchas not greater than 100 μm, and even not greater than 50 μm, such as notgreater than 25 μm and even not greater than 10 μm. These features canbe deposited by ink-jet printing of a single droplet or multipledroplets at-the same location with or without drying in betweendeposition of droplets or periods of multiple droplet deposition. In oneembodiment, the surface tension of the precursor composition on thesubstrate material is chosen to provide poor wetting of the surface sothat the composition contracts onto itself after printing. This providesa method for producing deposits with sizes equal to or smaller than thedroplet diameter.

The compositions and methods of the present invention can also be usedto form lines. In one embodiment, the lines can advantageously have anaverage width of not greater than 250 μm, such as not greater than 100μm, and even not greater than 50 μm.

The compositions and methods of the present invention produce featuresthat have good adhesion to the substrates on which they are formed. Forexample, the conductive features will adhere to the substrate with apeel strength of at least 10 newtons/cm. Adhesion can be measured usingthe scotch-tape test, wherein scotch-tape is applied to the feature andis pulled perpendicular to. the plane of the trace and the substrate.This applies a force of about 10 N/cm. A passing measure is when littleor no residue from the feature remains on the tape.

Applications

The low viscosity precursor compositions and methods of the presentinvention can advantageously be used in a variety of applications. Thefollowing is a non-limiting description of the types of devices andcomponents to which the methods and compositions of the presentinvention are applicable.

The compositions and methods of the present invention can be used tofabricate transparent antennas for RF (radio frequency) tags and smartcards. This is enabled by compositions comprising a transparentconductive metal oxide such as ITO. In another embodiment, thecompositions can include some metal to enhance conductivity. In oneembodiment, the antenna comprises a material with a sheet resistivity offrom about 10 to 100,000 ohms/square. In another embodiment, the antennacomprises a conductor with a resistivity that is not greater than threetimes the resistivity of substantially pure silver. High conductivitytraces are required for inductively coupled antennas whereas conductivemetal oxides can be used for electrostatic (capacitively coupled)antennas.

The compositions can also serve as solder replacements. Suchcompositions can include silver, lead or tin.

The compositions and methods can be utilized to provide connectionbetween chips and other components in smart cards and RF tags.

In one embodiment, the surface to be printed onto is not planar and anon-contact printing approach is used. The non-contact printing approachcan be ink-jet printing or another technique providing deposition ofdiscrete units of fluid onto the surface. Examples of surfaces that arenon-planar include in windshields, electronic components, electronicpackaging and visors.

The compositions and methods provide the ability to print disposableelectronics such as for games included in magazines. The compositionscan advantageously be deposited and reacted on cellulose-based materialssuch as paper or cardboard. The cellulose-based material can be coatedif necessary to prevent bleeding of the precursor composition into thesubstrate. For example, the cellulose-based material could be coatedwith a UV curable polymer.

The compositions and methods can be used to form under-bumpmetallization, redistribution patterns and basic circuit components.

The compositions and processes of the present invention can also be usedto fabricate microelectronic components such as multichip modules,particularly for prototype designs or low-volume production

Another technology where the direct-write deposition of electronicfeatures according to the present invention provides significantadvantages is for flat panel displays, such as plasma display panels.Ink-jet deposition of electronic powders is a particularly useful methodfor forming the electrodes for a plasma display panel. The electronicpowders and deposition method according to the present invention canadvantageously be used to form the electrodes, as well as the bus linesand barrier ribs, for the plasma display panel. Typically, a metal pasteis printed onto a glass substrate and is fired in air at from about 450°C. to 600° C. Direct-write deposition of low viscosity precursorcompositions offers many advantages over paste techniques includingfaster production time and the flexibility to produce prototypes andlow-volume production applications. The deposited features will havehigh resolution and dimensional stability, and will have a high density.

Another type of flat panel display is a field emission display (FED).The deposition method of the present invention can advantageously beused to deposit the microtip emitters of such a display. Morespecifically, a direct-write deposition process such as an ink-jetdeposition process can be used to accurately and uniformly create themicrotip emitters on the backside of the display panel.

Another type of electronic powder to which the present invention isapplicable is transparent electrode powder, particularly indium-tinoxide, referred to as ITO. Such materials are used as electrodes indisplay applications, particularly for thin-film electroluminescent(TFEL) displays. The electrode patterns of ITO can advantageously bedeposited using the direct-write method of the present inventionincluding an ink-jet, particularly to form discrete patterns of indicia,or the like.

The present invention is also applicable to inductor-based devicesincluding transformers, power converters and phase shifters. Examples ofsuch devices are illustrated in: U.S. Pat. Nos. 5,312,674 by Haertlinget al.; U.S. Pat. 5,604,673 by Washburn et al.; and U.S. Pat. No.5,828,271 by Stitzer. Each of the foregoing U.S. Patents is incorporatedherein by reference in their entirety. In such devices, the inductor iscommonly formed as a spiral coil of an electrically conductive trace,typically using a thick-film paste method. To provide the mostadvantageous properties, the metalized layer, which is typically silver,must have a fine pitch (line spacing). The output current can be greatlyincreased by decreasing the line width and decreasing the distancebetween lines. The direct-write process of the present invention isparticularly advantageous for forming such devices, particularly whenused in a low-temperature cofired ceramic package (LTCC).

The present invention can also be used to fabricate antennas such asantennas used for cellular telephones. The design of antennas typicallyinvolves many trial and error iterations to arrive at the optimumdesign. The direct-write process of the present invention advantageouslypermits the formation of antenna prototypes in a rapid and efficientmanner, thereby reducing a product development time. Examples ofmicrostrip antennas are illustratedlin: U.S. Pat. No. 5,121,127 byToriyama; U.S. Pat. No. 5,444,453 by Lalezari; U.S. Pat. No. 5,767,810by Hagiwara et al.; and U.S. Pat. No. 5,781,158 by Ko et al. Each ofthese U.S. patents is incorporated herein by reference in theirentirety. The methodology of the present invention can be used to formthe conductors of an antenna assembly.

The precursor compositions and methods of the present invention can alsobe used to apply underfill materials that are used below electronicchips to attach the chips to surfaces and other components. Hollowparticles are particularly advantageous because they are substantiallyneutrally buoyant. This allows the particles to be used in underfillapplications without settling of the particles in the liquid between thechip and surface below. Further, the spherical morphology of theparticles allows them to flow better through the small gap. Thissignificantly reduces the stratification that is often observed withdense particles. Further, very high thermal conductivity is not requiredand therefore silica is often used in this application. In otherapplications, the material must be thermally conductive but notelectrically conductive. Materials such as boron nitride (BN) can thenbe used.

Additional applications enabled by the low viscosity precursorcompositions and deposition methods of the present invention include lowcost or disposable electronic devices such as electronic displays,electrochromic, electrophoretic and light-emitting polymer-baseddisplays. Other applications include circuits imbedded in a wide varietyof devices such as low cost or disposable light-emitting diodes, solarcells, portable computers, pagers, cell phones and a wide variety ofinternet compatible devices such as personal organizers and web-enabledcellular phones. The present invention also enables a wide variety ofsecurity and authentication applications. For example, with the adventand growth of desktop publishing and color-photocopiers, theopportunities for document and coupon fraud have increased dramatically.The present invention has utility in a variety of areas including couponredemption, inventory security, currency security, compact disk securityand driver's license and passport security. The present invention canalso be utilized as an effective alternative to magnetic strips.Presently, magnetic strips include identification numbers such as creditcard numbers that are programmed at the manufacturer. These strips areprone to failure and are subject to fraud because they are easily copiedor modified. To overcome these shortcomings, circuits can be printed onthe substrate and encoded with specific consumer information. Thus, thepresent invention can be used to improve the security of credit cards,ATM cards and any other tracking card, which uses magnetic strips as asecurity measure.

The compositions and methods of the present invention can also produceconductive patterns that can be used in flat panel displays. Theconductive materials used for electrodes in display devices havetraditionally been manufactured by commercial deposition processes suchas etching, evaporation, and sputtering onto a substrate. In electronicdisplays it is often necessary to utilize a transparent electrode toensure that the display images can be viewed. Indium tin oxide (ITO),deposited by means of vacuum-deposition or a sputtering process, hasfound widespread acceptance for this application. U.S. Pat. No.5,421,926 by Yukinobu et al. discloses a process for printing ITO inks.For rear electrodes (i.e., the electrodes other than those through whichthe display is viewed) it is often not necessary to utilize transparentconductors. Rear electrodes can therefore be formed from conventionalmaterials and by conventional processes. Again, the rear electrodes havetraditionally been formed using costly sputtering or vacuum depositionmethods. The compositions according to the present invention allow thedirect deposition of metal electrodes onto low temperature substratessuch as plastics. For example, a silver precursor composition can beink-jet printed and heated at 150° C. to form 150 μm by 150 μm squareelectrodes with excellent adhesion and sheet resistivity values of lessthan 1 ohms per square.

In one embodiment, the precursor compositions are used to interconnectelectrical elements on a substrate, such as non-linear elements.Non-linear elements are defined herein as electronic devices thatexhibit nonlinear responses in relationship to a stimulus. For example adiode is known to exhibit a nonlinear output-current/input-voltageresponse. An electroluminescent pixel is known to exhibit a non-linearlight-output/applied-voltage response. Nonlinear devices also includebut are not limited to transistors such as TFTs and OFETs, emissivepixels such as electroluminescent pixels, plasma display pixels, fieldemission display (FED) pixels and organic light emitting device (OLED)pixels, non emissive pixels such as reflective pixels includingelectrochromic material, rotatable microencapsulated microspheres,liquid crystals, photovoltaic elements, and a wide range of sensors suchas humidity sensors.

Nonlinear elements, which facilitate matrix addressing, are an essentialpart of many display systems. For a display of M×N pixels, it isdesirable to use a multiplexed addressing scheme whereby M columnelectrodes and N row electrodes are patterned orthogonally with respectto each other. Such a scheme requires only M+N address lines (as opposedto M×N lines for a direct-address system requiring a separate addressline for each pixel). The use of matrix addressing results insignificant savings in terms of power consumption and cost ofmanufacture. As a practical matter, the feasibility of using matrixaddressing usually hinges upon the presence of a nonlinearity in anassociated device. The nonlinearity eliminates crosstalk betweenelectrodes and provides a thresholding function. A traditional way ofintroducing nonlinearity into displays has been to use a backplanehaving devices that exhibit a nonlinear current/voltage relationship.Examples of such devices include thin-film transistors (TFT) andmetal-insulator-metal (MIM) diodes. While these devices achieve thedesired result, they involve thin-film processes, which suffer from highproduction costs as well as relatively poor manufacturing yields.

The present invention allows the direct printing of the conductivecomponents of nonlinear devices including the source the drain and thegate. These nonlinear devices may include directly printed organicmaterials such as organic field effect transistors (OFET) or organicthin film transistors (OTFT), directly printed inorganic materials andhybrid organic/inorganic devices such as a polymer based field effecttransistor with an inorganic gate dielectric. Direct printing of theseconductive materials will enable low cost manufacturing of large areaflat displays.

The compositions and methods of the present invention produce conductivepatterns that can be used in flat panel displays to form the addresslines or data lines. The lines may be made from transparent conductingpolymers, transparent conductors such as ITO, metals or other suitableconductors. The present invention provides ways to form address and datalines using deposition tools such as an ink-jet device. The precursorcompositions of the present invention allow printing on large areaflexible substrates such as plastic substrates and paper substrates,which are particularly useful for large area flexible displays. Addresslines may additionally be insulated with an appropriate insulator suchas a non-conducting polymer or other suitable insulator. Alternatively,an appropriate insulator may be formed so that there is electricalisolation between row conducting lines, between row and column addresslines; between column address lines or for other purposes. These linescan be printed with a thickness of about one μm and a line width of 100μm by ink-jet printing the precursor composition. These data lines canbe printed continuously on large substrates with an uninterrupted lengthof several meters. Surface modification can be employed, as is discussedabove, to confine the composition and to enable printing of lines asnarrow as 10 μm. The deposited lines can be heated to 200° C. to formmetal lines with a bulk conductivity that is not less than 10 percent ofthe conductivity of the equivalent pure metal.

Flat panel displays may incorporate emissive or reflective pixels. Someexamples of emissive pixels include electroluminescent pixels,photoluminescent pixels such as plasma display pixels, field emissiondisplay (FED) pixels and organic light emitting device (OLED) pixels.Reflective pixels include contrast media that can be altered using anelectric field. Contrast media may be electrochromic material, rotatablemicroencapsulated microspheres, polymer dispersed liquid crystals(PDLCs), polymer stabilized liquid crystals, surface stabilized liquidcrystals, smectic liquid crystals, ferroelectric material, or othercontrast media well known in art. Many of these contrast media utilizeparticle-based non-emissive systems. Examples of particle-basednon-emissive systems include encapsulated electrophoretic displays (inwhich particles migrate within a dielectric fluid under the influence ofan electric field); electrically or magnetically driven rotating-balldisplays as disclosed in U.S. Pat. Nos. 5,604,027 and 4,419,383, whichare incorporated herein by reference in their entirety; and encapsulateddisplays based on micromagnetic or electrostatic particles as disclosedin U.S. Pat. Nos. 4,211,668, 5,057,363 and 3,683,382, which areincorporated herein by reference in their entirety. A preferred particlenon-emissive system is based on discrete, microencapsulatedelectrophoretic elements, examples of which are disclosed in U.S. Pat.No. 5,930,026 by Jacobson et al. which is incorporated herein byreference in its entirety. In one embodiment, the present inventionrelates to directly printing conductive features, such as electricalinterconnects and electrodes for addressable, reusable, paper-likevisual displays. Examples of paper-like visual displays include“gyricon” (or twisting particle) displays and forms of electronic papersuch as particulate electrophoretic displays (available from E-inkCorporation, Cambridge, Mass.). A gyricon display is an addressabledisplay made up of optically anisotropic particles, with each particlebeing selectively rotatable to present a desired face to an observer.For example, a gyricon display can incorporate “balls” where each ballhas two distinct hemispheres, one black and the other white. Eachhemisphere has a distinct electrical characteristic (e.g., zetapotential with respect to a dielectric fluid) so that the ball iselectrically as well as optically anisotropic. The balls areelectrically dipolar in the presence of a dielectric fluid and aresubject to rotation. A ball can be selectively rotated within itsrespective fluid-filled cavity by application of an electric field, soas to present either its black or white hemisphere to an observerviewing the surface of the sheet.

In another embodiment, the present invention relates to electricalinterconnects and electrodes for organic light emitting displays(OLEDs). Organic light emitting displays are emissive displaysconsisting of a transparent substrate coated with a transparentconducting material (e.g., ITO), one or more organic layers and acathode made by evaporating or sputtering a metal of low work functioncharacteristics (e.g., calcium or magnesium). The organic layermaterials are chosen so as to provide charge injection and transportfrom both electrodes into the electroluminescent organic layer (EL),where the charges recombine to emit light. There may be one or moreorganic hole transport layers (HTL) between the transparent conductingmaterial and the EL, as well as one or more electron injection andtransporting layers between the cathode and the EL. The precursorcompositions according to the present invention allow the directdeposition of metal electrodes onto low temperature substrates such asflexible large area plastic substrates that are particularly preferredfor OLEDs. For example, a metal precursor composition can be ink-jetprinted and heated at 150° C. to form a 150 μm by 150 μm squareelectrode with excellent adhesion and a sheet resistivity value of lessthan 1 ohm per square. The compositions and printing methods of thepresent invention also enable printing of row and column address linesfor OLEDs. These lines can be printed with a thickness of about one μmand a line width of 100 μm using ink-jet printing. These data lines canbe printed continuously on large substrates with an uninterrupted lengthof several meters. Surface modification can be employed, as is discussedabove, to confine the precursor composition and to enable printing ofsuch lines as narrow as 10 μm. The printed ink lines can be heated to150° C. and form metal lines with a bulk conductivity that is no lessthan 5 percent of the conductivity of the equivalent pure metal.

In one embodiment, the present invention relates to electricalinterconnects and electrodes for liquid crystal displays (LCDs),including passive-matrix and active-matrix. Particular examples of LCDsinclude twisted nematic (TN), supertwisted nematic (STN), doublesupertwisted nematic (DSTN), retardation film supertwisted nematic(RFSTN), ferroelectric (FLCD), guest-host (GHLCD), polymer-dispersed(PD), polymer network (PN).

Thin film transistors (TFTs) are well known in the art, and are ofconsiderable commercial importance. Amorphous silicon-based thin filmtransistors are used in active matrix liquid crystal displays. Oneadvantage of thin film transistors is that they are inexpensive to make,both in terms of the materials and the techniques used to make them. Inaddition to making the individual TFTs as inexpensively as possible, itis also desirable to inexpensively make the integrated circuit devicesthat utilize TFTs. Accordingly, inexpensive methods for fabricatingintegrated circuits with TFTs, such as those of the present invention,are an enabling technology for printed logic.

For many applications, inorganic interconnects are not adequatelyconductive to achieve the desired switching speeds of an integratedcircuit due to high RC time constants. Printed pure metals, as enabledby the precursor compositions of the present invention, achieve therequired performance. A metal interconnect printed by using a silverprecursor composition as disclosed in the present invention will resultin a reduction of the resistance (R) and an associated reduction in thetime constant (RC) by a factor of 100,000, more preferably by 1,000,000,as compared to current conductive polymer interconnect material used toconnect polymer transistors.

Field-effect transistors (FETs), with organic semiconductors as activematerials, are the key switching components in contemplated organiccontrol, memory, or logic circuits, also referred to as plastic-basedcircuits. An expected advantage of such plastic electronics is theability to fabricate them more easily than traditional silicon-baseddevices. Plastic electronics thus provide a cost advantage in caseswhere it is not necessary to attain the performance level and devicedensity provided by silicon-based devices. For example, organicsemiconductors are expected to be much more readily printable thanvapor-deposited inorganics, and are also expected to be less sensitiveto air than recently proposed solution-deposited inorganic semiconductormaterials. For these reasons, there have been significant effortsexpended in the area of organic semiconductor materials and devices.

Organic thin film transistors (TFTs) are expected to become keycomponents in the plastic circuitry used in display drivers of portablecomputers and pagers, and memory elements of transaction cards andidentification tags. A typical organic TFT circuit contains a sourceelectrode, a drain electrode, a gate electrode, a gate dielectric, aninterlayer dielectric, electrical interconnects, a substrate, andsemiconductor material. The precursor compositions of the presentinvention can be used to deposit all the components of this circuit,with the exception of the semiconductor material.

One of the most significant factors in bringing organic TFT circuitsinto commercial use is the ability to deposit all the components on asubstrate quickly, easily and inexpensively as compared with silicontechnology (i.e., by reel-to-reel printing). The precursor compositionsof the present invention enable the use of low cost depositiontechniques, such as ink-jet printing, for depositing these components.

The precursor compositions of the present invention are particularlyuseful for the direct printing of electrical connectors as well asantennae of smart tags, smart labels, and a wide range of identificationdevices such as radio frequency identification (RFID) tags. In a broadsense, the conductive precursor compositions can be utilized forelectrical connection of semiconductor radio frequency transceiverdevices to antenna structures and particularly to radio frequencyidentification device assemblies. A radio frequency identificationdevice (“RFID”) by definition is an automatic identification and datacapture system comprising readers and tags. Data is transferred usingelectric fields or modulated inductive or radiating electromagneticcarriers. RFID devices are becoming more prevalent in suchconfigurations as, for example, smart cards, smart labels, securitybadges, and livestock tags.

The precursor compositions of the present invention also enable the lowcost, high volume, highly customizable production of electronic labels.Such labels can be formed in various sizes and shapes for collecting,processing, displaying and/or transmitting information related to anitem in human or machine readable form. The precursor compositions ofthe present invention can be used to print the conductive featuresrequired to form the logic circuits, electronic interconnections,antennae, and display features in electronic labels. The electroniclabels can be an integral part of a larger printed item such as alottery ticket structure with circuit elements disclosed in a pattern asdisclosed in U.S. Pat. No. 5,599,046.

In another embodiment of the present invention; the conductive patternsmade in accordance with the present invention can be used as electroniccircuits for making photovoltaic panels. Currently, conventionalscreen-printing is used in mass scale production of solar cells.Typically, the top contact pattern of a solar cell consists of a set ofparallel narrow finger lines and wide collector lines depositedessentially at a right angle to the finger lines on a semiconductorsubstrate or wafer. Such front contact formation of crystalline solarcells is performed with standard screen-printing techniques. Directprinting of these contacts with the precursor compositions of thepresent invention provides the advantages of production simplicity,automation, and low production cost.

Low series resistance and low metal coverage (low front surfaceshadowing) are basic requirements for the front surface metallization insolar cells. Minimum metallization widths of 100 to 150 μm are obtainedusing conventional screen-printing. This causes a relatively highshading of the front solar cell surface. In order to decrease theshading, a large distance between the contact lines, i.e., 2 to 3 mm isrequired. On the other hand, this implies the use of a highly doped,conductive emitter layer. However, the heavy emitter doping induces apoor response to short wavelength light. Narrower conductive lines canbe printed using the precursor composition and printing methods of thepresent invention. The conductive precursor compositions of the presentinvention enable direct printing of finer features down to 20 μm. Theprecursor compositions of the present invention further enable theprinting of pure metals with resistivity values of the printed featuresas low as 2 times bulk resistivity after processing at temperatures aslow as 200° C.

The low processing and direct-write deposition capabilities according tothe present invention are particularly enabling for large area solarcell manufacturing on organic and flexible substrates. This isparticularly useful in manufacturing novel solar cell technologies basedon organic photovoltaic materials such as organic semiconductors and dyesensitized solar cell technology as disclosed in U.S. Pat. No. 5,463,057by Graetzel et al. The precursor compositions according to the presentinvention can be directly printed and heated to yield a bulkconductivity that is no less than 10 percent of the conductivity of theequivalent pure metal, and achieved by heating the printed features attemperatures below 200° C. on polymer substrates such as plexiglass(PMMA).

Another embodiment of the present invention enables the production of anelectronic circuit for making printed wiring board (PWBs) and printedcircuit boards (PCBs). In conventional subtractive processes used tomake printed-wiring boards, wiring patterns are formed by preparingpattern films. The pattern films are prepared by means of a laserplotter in accordance with wiring pattern data outputted from a CAD(computer-aided design system), and are etched on copper foil by using aresist ink or a dry film resist.

In such conventional processes, it is necessary to first form a patternfilm, and to prepare a printing plate in the case when a photo-resistink is used, or to take the steps of lamination, exposure anddevelopment in the case when a dry film resist is used.

Such methods can be said to be methods in which the digitized wiringdata are returned to an analog image-forming step. Screen-printing has alimited work size because of the printing precision of the printingplate. The dry film process is a photographic process and, although itprovides high precision, it requires many steps, resulting in a highcost especially for the manufacture of small lots.

The precursor composition and printing methods of the present inventionoffer solutions to overcome the limitations of the current PWB formationprocess. For example, they do not generate any waste. The printingmethods of the present invention are a single step direct printingprocess and are compatible with small-batch and rapid turn aroundproduction runs. For example, a copper precursor composition can bedirectly printed onto FR4 (a polymer impregnated fiberglass) to forminterconnection circuitry. These features are formed by heating theprinted copper precursor in an N₂ ambient at 150° C. to form copperlines with a line width of not greater than 100 μm, a line thickness ofnot greater than 5 μm, and a bulk conductivity that is not less than 10percent of the conductivity of the pure copper metal.

Patterned electrodes obtained by one embodiment of the present inventioncan also be used for screening electromagnetic radiation or earthingelectric charges, in making touch screens, radio frequencyidentification tags, electrochromic windows and in imaging systems,e.g., silver halide photography or electrophotography. A device such asthe electronic book described in U.S. Pat. No. 6,124,851 can be formedusing the compositions of the present invention.

EXAMPLES

The following examples illustrate the many advantages of the lowviscosity precursor compositions according to the present invention. Forreference purposes, pure Ag-trifluoroacetate has a normal decompositiontemperature of about 325° C. as indicated by thermogravimetric analysis.Pure Ag-acetate decomposes at about 255° C. As used in these examples,thermogravimetric analysis consisted of heating samples (typically 50milligrams) in air at a heating rate of 10° C./minute and observing theweight loss of the sample.

Example 1

Comparative Example

A silver metal precursor composition containing 50 gramsAg-trifluoroacetate and 50 grams H₂O was formulated. The calculatedsilver content of the precursor composition was 24.4 wt. % andthermogravimetric analysis showed the mass loss reached 78 wt. % at 340°C. This data corresponds to the above-described decompositiontemperature for pure Ag-trifluoroacetate, within a reasonable margin forerror.

Example 2

Preferred Additive

A silver precursor composition was formulated containing 44 gramsAg-trifluoroacetate, 22 grams H₂O, 33 grams DEGBE and 1 gram lacticacid. The calculated silver content was 21.5 wt. % and thermogravimetricanalysis showed the mass loss reached 79 wt. % at 215EC. The addition ofDEGBE as a conversion reaction inducing agent advantageously reduced theconversion temperature by 125EC compared to the formulation described inExample 1, a decrease of about 34 percent compared to pureAg-trifluoracetate. The lactic acid functions as a crystallizationinhibitor.

Example 3

Comparative Example

A silver precursor composition was formulated containing 58 gramsAg-trifluoroacetate and 42 grams dimethylformamide. The calculatedsilver content was 21.5 wt. % and thermogravimetric analysis showed amass loss of 78.5 wt. % at 335EC, a conversion temperature similar tothe formulation in Example 1. This example illustrates that a commonsolvent (dimethylformamide) had no affect on the conversion temperatureof the composition.

Example 4

(Preferred Solvent)

A silver precursor composition was formulated containing 64.8 gramsAg-trifluoroacetate, 34 grams DMAc and 1.1 grams of a styrene allylalcohol (SAA) copolymer binder. Thermogravimetric analysis showed thatprecursor conversion to silver was complete at 275° C. The use of DMAcreduced the conversion temperature by about 65° C. as compared toExample 1.

Example 5

A silver precursor composition was formulated containing 51 gramsAg-trifluoroacetate, 16 grams DMAc and 32 grams alpha-terpineol. Thecalculated silver content was 25 wt. %. Thermogravimetric analysisshowed a mass loss of 77 wt. % at 205EC. Compared to the compositiondescribed in Example 4, which does not employ alpha-terpineol as anadditive, the conversion temperature was further reduced by 70° C.

Example 6

A silver precursor composition was formulated containing 33.5 gramsAg-trifluoroacetate, 11 grams DMAc, 2 grams lactic acid and 53.5 gramsDEGBE. The calculated silver content was 16.3 wt. %. Thermogravimetricanalysis showed a mass loss of 83 wt. % at 205° C. to 215° C. Thedecomposition temperature is 60° C. to 70° C. lower as compared to thecomposition described in Example 4, which does not employ DEGBE as anadditive in addition to DMAc.

Example 7

A silver precursor composition was formulated containing 49 gramsAg-trifluoroacetate, 16 grams DMAc, 32 grams alpha-terpineol and 1.2grams Pd-acetate. Thermogravimetric analysis indicated completeconversion of the metal organic precursors at 170° C. This conversiontemperature is 35EC lower as compared to the composition described inExample 5, which does not employ Pd-acetate as a further additive.

Example 8

A silver precursor composition was formulated containing 46 gramsAg-trifluoroacetate, 49 grams DMAc and 2.3 grams Pd-acetate.Thermogravimetric analysis indicated complete conversion of the metalorganic precursors at 195° C. This conversion temperature is 80° C.lower compared to the composition described in Example 4, which does notemploy Pd-acetate as a further additive.

Example 9

A silver precursor composition was formulated containing 6.8 gramsAg-acetate and 93.1 grams ethanolamine. Thermogravimetric analysisshowed that precursor conversion to silver was complete at 190° C. Thisconversion temperature is 65° C. lower than the conversion temperatureof pure Ag-acetate.

Example 10

A silver/palladium precursor composition was formulated containing 8.2grams Ag-trifluoroacetate, 18.7 grams Pd-trifluoroacetate, 70.2 gramsDMAc and 2.8 grams lactic acid. The targeted ratio of Ag/Pd was 40/60 bymass. The calculated Ag/Pd content of the precursor composition was 10wt. %. Thermogravimetric analysis showed a mass loss of 87 wt. % at 190°C. The presence of Pd-trifluoroacetate reduced the conversiontemperature by 80° C. compared to the composition described in Example4.

Example 11

A silver/palladium precursor composition was formulated containing 5.2grams Ag-trifluoroacetate, 23.4 grams Pd-trifluoroacetate, 67.9 gramsDMAc and 3.5 grams lactic acid. The targeted ratio of Ag/Pd was 25/75 bymass and the calculated Ag/Pd content was 10 wt.%. Thermogravimetricanalysis showed a mass loss of 88 wt. % at 190° C. The presence ofPd-trifluoroacetate reduced the conversion temperature by 80EC comparedto the composition described in Example 4.

Example 12

Silver precursor compositions containing various amounts and ratios ofAg-neodecanoate, solvents and additives were formulated. Specificexamples are outlined in Table 9. In general, the differences indecomposition temperature are not as pronounced as in formulationscontaining Ag-trifluoroacetate. Typically, compositions containingAg-neodecanoate in either DMAc or NMP, together with DEGBE orethyleneglycolbutylether and/or alpha-terpineol as additives resulted indecomposition temperatures that are between 40° C. and 55° C. lower thanpure Ag-neodecanoate. Xylene had no affect on the decompositiontemperature of the Ag-neodecanoate. TABLE 9 Examples UtilizingAg-Neodecanoate DECOMPOSITION TEMPERATURE RUN SOLVENT ADDITIVE 1ADDITIVE 2 (° C.) Ag neodecanoate 265 Ag neodecanoate Xylene 265 Agneodecanoate DMAc Methoxyethanol 250 7.6 × 10⁻² mole 7.9 × 10⁻² mole1.45 × 10⁻² mole Ag neodecanoate Xylene 1-Butanol 250 1.52 × 10⁻² mole3.58 × 10⁻² mole 2.67 × 10⁻² mole Ag neodecanoate DMAc DEGBE 220-230 7.6× 10⁻² mole 6.43 × 10⁻² mole 1.48 × 10⁻² mole Ag DMAc DEGBEAlpha-Terpineol 210-230 neodecanoate 2.66 × 10⁻² 6.43 × 10⁻² mole 2.95 ×10⁻² mole 5.19 × 10⁻² mole mole Ag neodecanoate DMAc DEGBE EGBE 225 1.14× 10⁻² mole 2.64 × 10⁻² mole 3.1 × 10⁻² mole 1.69 × 10⁻² mole Agneodecanoate DMAc EGBE 240 1.14 × 10⁻² mole 5.05 × 10⁻² mole 2.2 × 10⁻²mole Ag neodecanoate THF EGBE 240 1.14 × 10⁻² mole 6.1 × 10⁻² mole 2.2 ×10⁻² mole Ag neodecanoate Xylene DEGBE 230 1.55 × 10⁻⁵ mole 2.92 × 10⁻²mole 1.79 × 10⁻² mole Ag neodecanoate NMP Ethanolamine 220 9.5 × 10⁻²mole 6.45 × 10⁻² mole 1.8 × 10⁻² mole Ag neodecanoate THF Methoxyethanol250 1.5 × 10⁻² mole 5.27 × 10⁻² mole 2.89 × 10⁻² mole

Example 13

A gold containing precursor composition was prepared containing 5 gramshydrated gold hydroxide, 15 ml acetic acid and 3 ml trifluoroaceticacid. The mixture was heated to 53° C. for 24 hours until all goldhydroxide had dissolved. The solution was filtered through a microfilterand a clear golden solution of the gold precursor was obtained.Thermogravimetric analysis showed that precursor conversion to gold wascomplete at 125° C.

Example 14

A gold containing precursor composition was prepared containing 5 gramshydrated gold hydroxide, and 18 ml trifluoroacetic acid. The mixture washeated to 53° C. for 3 hours and subsequently stirred at roomtemperature for 21 hours until all gold hydroxide has dissolved. Thesolution was filtered through a microfilter and a clear purple solutionof the gold precursor was obtained. Thermogravimetric analysis showedthat precursor conversion to gold started at room temperature and wascomplete at a conversion temperature of 90° C.

Example 15

A silver precursor composition was formulated containing 48.1 gramsAg-trifluoroacetate, 48.1 grams DMAc and 3.8 grams DEGBE. The precursorcomposition was deposited on a glass substrate and fired on a hotplateat 200° C. The resulting film showed large crystal growth and was notconductive. This was believed to be due to crystallization of theAg-trifluoracetate.

Example 16

A silver precursor composition was formulated containing 48.1 gramsAg-trifluoroacetate, 48.1 grams DMAc and 3.8 grams lactic acid as acrystallization inhibitor. The composition was deposited on a glasssubstrate and fired on a hotplate at 200° C. The resulting film showedreduced crystal growth, demonstrating the effectiveness of lactic acidas a crystallization inhibitor.

Example 17

A silver-precursor composition was formulated containing 33.5 gramsAg-trifluoroacetate, 11.2 grams DMAc, 53.6 grams DEGBE and 1.8 gramslactic acid. The composition was deposited on a polyimide substrate(KAPTON HN,.E.I. duPont deNemours Corp., Wilmington, Del.) using aninkjet device. The resulting film showed severe spreading and formedareas that no longer resembled the original pattern. This exampleillustrates that additional additives may be necessary to controlspreading of the precursor composition.

Example 18

A silver precursor composition was formulated containing 372 gramsAg-trifluoroacetate, 26.7 grams DMAc, 0.9 grams lactic acid, 34.5 gramsDEGBE and 0.9 grams SAA to control spreading. The composition wasdeposited on a polyimide substrate (KAPTON HN) using an ink-jet device.No spreading was observed. After heating in an oven at 250° C. theresulting film showed some shrinkage and had a bulk resistivity of 5.2times the resistivity of bulk silver.

Example 19

A silver precursor composition was formulated including 21.6 gramsAg-trifluoroacetate, 35.1 grams silver nanoparticles, 21.6 gramsethylene glycol and 21.6 grams water. All weight percentages arerelative to the weight of the final composition. The composition wasdeposited using an ink-jet device and the deposited precursor was heatedat 220° C. for 10 minutes to form a conductive trace.

Example 20

A silver precursor composition was formulated including 27.5 gramsAg-trifluoroacetate, 17.7 grams silver nanoparticles, 9.4 grams DMAc,43.9 grams DEGBE and 1.5 grams lactic acid. The composition wasdeposited using an ink-jet device and the deposited precursor was heatedto 220° C. for 10 minutes to form a conductive trace having aresistivity of not more than about 10 times the resistivity of pure bulksilver.

Precursor Solubility

Solubility of precursor material in a variety of different solvents wastested. Test solutions were prepared by dissolving the precursor in therespective solvent. Small amounts of solid precursor were addedincrementally and the solution shaken for 10 to 30 minutes. When thesolubility limit was reached by this method the solution was shaken for12 hours and re-evaluated. This procedure was repeated until additionalprecursor did not-dissolve or precipitation occurred. Solvents testedincluded water, toluene, xylene, N-methylpyrrolidinone (NMP),alpha-terpineol, N,N-dimethylacetamide (DMAc), N-methylacetamide,nitromethane, diethyleneglycolbutylether (DEGBE),triethyleneglycoldiethylether, methylalcohol, ethyl alcohol, isopropylalcohol, 1-butyl alcohol, methyl ethyl ketone, acetone, diethylether,tetrahydrofurane, ethanolamine, 3-amino-1-propanol, pyridine,diethylentriamine, tetraethylenediamine, 2-amino-butanol,isopropylaminoethanol.

In general, high solubilities were observed in particular forfluorinated metal carboxylates, mixed carboxylates as well as long chaincarboxylates. Preferred solvents for these compounds with regard tosolubility are toluene, xylene, N-Methyl pyrrolidinone, tetrahydrofuraneand DMAc. Also, some precursors can be successfully dissolved in highamounts in water. A particularly preferred combination consists ofsilver trifluoroacetate in DMAc where solutions with up to 78 wt. %precursor loading can be achieved.

Example 21

Ratio of Precursor to Reducing Agent

DMAc based silver precursor compositions were formulated containingdifferent ratios of Ag-trifluoroacetate and DEGBE. As illustrated inTable 10 thermogravimetric analysis showed that the higher the ratio ofDEGBE to Ag-trifluoroacetate, the lower the conversion temperature tosilver. A molar ratio of 1.2 —slightly above the stoichiometric ratio ofDEGBE to AG precursor—produces a conversion temperature to silver of210° C. The use of DEGBE reduced the decomposition temperature by about65° C. as compared to Example are incorporated in Table 10 forreference, where no DEGBE was used. of DEGBE to Ag-trifluoroacetate hada decreased effect on lowering the conversion temperature. TABLE 10Effect of Ratio of DEGBE to Ag-trifluoroacetate DEGBEAg-trifluoroacetate Conversion temperature (pbw) (pbw) (° C.) 0 40 27530 100 285 38 59 270 26.5 50 245 38 41 250 45 46 240 53.5 33.5 205-215

Example 22

Conductivity as Function of Time and Temperature

A precursor composition was formulated containing 37 gramsAg-trifluoroacetate, 34.5 grams DEGBE, 26.7 grams DMAc, 0.9 grams SAAcopolymer and 0.9 grams lactic acid and the composition was applied toglass slides to form thin films. These slides were then placed into apreheated oven and heated for controlled lengths of time vary from 1minute to 60 minutes. The oven was heated to temperatures ranging from130EC. to 250EC. As is illustrated in Table 11, the precursorcomposition formed conductive features at 200° C. after 10 minutes in aconvection oven. The numbers listed in Table 11are the resistivityexpressed as a multiple of the resistivity of bulk silver (“no”indicates a complete lack of conductivity). The most conductive featureswere formed and the most complete conversion occurred at 250° C. TABLE11 Resistivity as a Function of Time and Temperature Time (mins)Temperature (° C.) 1 2 5 7 10 30 60 130 No no No no no no no 150 No noNo no no no no 175 No no No no no no no 200 No no no no yes yes yes 220No no no no no yes/no yes 250 No no 850.5 161.8 119.3 5.2 5.8

The precursor composition does not form highly conductive featuresunless exposed to temperatures above 200° C. for a period of time. Thehighest conductivities are achieved when the composition is exposed to250° C. for 10 minutes or greater. Thermogravimetric analysis shows thatthe composition shows complete conversion at about 220° C. Samples thatare fired below 200° C. tended to form crystalline deposits caused byevaporation of the solvent before the desired reactions occurred. Theformation of crystals is more of a problem in convection ovens due tothe mass transfer from the films to the air. This transfer does notoccur in a box furnace. The samples heated in the box furnace tend tostay moist longer and not form crystals. The solutions formed elementalsilver as shown by x-ray diffraction (XRD) analysis.

The above indicates that one can achieve similar conductivities throughheating in an oven, or by any other conventional method by varyingeither the time or the temperature. If one wishes to achieve a givenconductivity all one has to do is fire for a short time at an elevatedtemperature. If it is desired to fire at lower temperatures one can fireat extended periods of time at a lower temperature. The resultingmaterials should not differ substantially.

Ink-Jet Deposition of Features

Example 23

A silver precursor composition was formulated comprising 1.2 gramsstyrene allyl alcohol, 49.2 grams DMAc, 46.2 grams Ag-trifluoroacetate,1.4 grams lactic acid and 2.1 grams Pd-trifluoroacetate. The compositionhad a viscosity of 14 centipoise at a shear rate of 66 Hz. The surfacetension was 37.4 dynes/cm. The composition was deposited using anink-jet device and the deposited precursor was heated to 250° C. to formsubstantially pure metal traces that were conductive. Thermogravimetricanalysis indicated that decomposition was substantially complete at 230°C.

This example illustrates an ink-jettable composition and the use ofPd-trifluoroacetate as a reducing agent for the Ag-trifluoroacetate.This composition has excellent adhesion to KAPTON-HN, silicon and glasssubstrates.

Example 24

A silver precursor composition was formulated comprising 1.8 gramsstyrene allyl alcohol, 54.2 grams N-Methyl pyrolidone, 40.5 gramsAg-trifluoroacetate, 2.6 grams lactic acid and 0.9 grams Pd-trifluoroacetate. The composition had a viscosity of 16 centipoise at ashear rate of 66 Hz. The surface tension was 40 dynes/cm. Thecomposition was deposited using an ink-jet device and the depositedprecursor was heated to 250° C. to form substantially pure metal tracesthat were conductive. Thermogravimetric analysis indicates thatdecomposition is substantially complete at 225° C.

This is an example of an ink-jettable composition and of the use ofPd-trifluoroacetate as a reducing agent for Ag-trifluoroacetate. Thisexample also indicates the wide range of solvents usable for this typeof application. This composition has excellent adhesion to KAPTON-HN,silicon and glass.

Example 25

A silver precursor composition was formulated comprising 1.3 gramsstyrene allyl alcohol, 46.7 grams DMAc, 42.5 grams Ag-trifluoroacetate,2.6 grams lactic acid and 6.9 grams Pd-trifluoroacetate. Thiscomposition had a viscosity of 16.9 centipoise at a shear rate of 66 Hz.The surface tension was 37.8 dynes/cm. The composition was depositedusing and ink-jet device and the deposited precursor was heated to 250°C. to form substantially pure metal traces that were conductive.Thermagravimetric analysis indicated that decomposition wassubstantially complete at 205° C.

This is an example of an ink-jettable composition and of the use ofPd-trifluoroacetate as a reducing agent for Ag-trifluoroacetate. Thiscomposition has excellent adhesion to KAPTON-HN, silicon, and glass.

Example 26

A silver precursor and silver nanoparticle precursor composition wasformulated comprising 31.6 grams Ag-trifluoroacetate, 31.6 grams water,30.9 grams ethylene glycol and 5.9 grams silver nanoparticles. Thecomposition had a viscosity of 10 centipoise at a shear rate of 66Hz andthe surface tension was 51 dynes/cm. The composition was deposited usingan ink-jet device and heated to 100° C. to produce traces that wereconductive and phase pure silver as measured by XRD. The composition wasalso deposited using an ink-jet device and heated to 200° C. to producetraces that were conductive and were phase pure silver by XRD.Thermogravimetric analysis indicates that conversion was complete byabout 185C. This is an example of a precursor and nanoparticleformulation that can be deposited by an ink-jet and heated at lowtemperatures to produce phase pure silver on low temperature substrates.

Example 27

A silver precursor composition was formulated comprising 33 gramsAg-trifluoroacetate, 33 grams DMAc, 33 grams diethylene glycol butylether (DEGBE), and 3 grams lactic acid. The composition had a viscosityof 10 centipoise at a shear rate of 66 Hz and the surface tension was 63dynes/cm. This composition was deposited using an ink-jet and heated to200° C. for 30 minutes. The resulting features were phase pure silver byXRD. Thermogravimetric analysis indicated complete conversion at 210C.when heated at 10° C./min. This same composition, when deposited andheated at 250° C. for 10 minutes, produced traces that were phase puresilver by XRD, and had a bulk resistivity of not greater than 4 timesthat of bulk silver. This composition has excellent adhesion to glass,KAPTON-HN, silicon nitrite and silicon.

Example 28

A silver precursor composition was formulated comprising 38.3 gramsAg-Trifluoroacetate, 29.2 grams DMAc, 29.2 grams DEGBE, and 3.4 gramslactic acid. This composition, when deposited and heated to 250° C.,produced phase pure silver that was highly conductive. This compositionhas excellent adhesion to glass, KAPTON-HN, silicon nitrite and silicon.

Example 29

A silver nanoparticle composition was formulated comprising 16.6 gramssilver nanoparticles, 41.7 grams water and 41.7 grams ethylene glycol.This composition was deposited using an ink-jet and, when heated to 100°C. on paper and KAPTON-HN, formed conductive traces that were phase puresilver by XRD. This is an example of a purely particle based compositionthat can be deposited onto low temperature substrates such as mylar,paper and others.

Example 30

A silver nanoparticle composition was formulated comprising 46.7 silvernanoparticles, 17.8 grams water, 17.8 grams Ag-trifluoroacetate and 17.8grams ethylene glycol. This composition, when deposited and heated,formed phase pure silver by XRD that was highly conductive.

Example 31

A silver nanoparticle composition was formulated comprising 35 gramsethyl alcohol and 65 grams silver nanoparticles. This composition, whenheated on a glass slide at 70° C. for 4 hours, produced traces that wereconductive, phase pure silver by XRD, and had a bulk resistivity of 100times that of bulk silver. This composition, when deposited with anink-jet device, produced traces that were phase pure silver by XRD. Thisillustrates an example of an ultra low temperature silver composition.

Copper Precursor Compositions

Example 32

Copper formate xH₂O (x˜2) was analyzed by thermogravimetric analysis andwas shown to undergo full decomposition to copper by about 225° C. ineach of forming gas, air and nitrogen. The example in air showed thatfull decomposition to copper takes place before copper oxides begin toform.

Example 33

Copper formate×6H₂O found to have a solubility in water of about 6% byweight forming a light blue solution. Droplets were deposited onto glassslide. Deposits form copper when processed on hotplate at 200° C. undernitrogen flow gas. Boiling of solvent causes some splattering and dryingof solvent causes recrystallization of salt and leads to slowdecomposition and formation of disconnected copper deposit. This showsthat additives are necessary to increase solubility of copper anddecrease volatility of solution to allow for good film formation.

Example 34

Complexing agents for copper formate were added to aqueous solutions.Examples of complexing agents used are ammonium hydroxide, ethanolamine,ethylene diamene, 3-amino-1-propanol, 2-amino-1-butanol,2-(isopropylamino)ethanol, and triethanolamine. The addition of thesecomplexing agents increased the solubility of copper formate andproduced a visible color change. The resulting solutions were made asconcentrated as possible and were decomposed from 160° C. to 200° C. ona hotplate under nitrogen flow. The higher vapor pressure complexingagents such as ammonium hydroxide tended to boil and splatter, producingdisconnected films with some “halo” of vapor deposition. The lower vaporpressure complexing agents such as 3-amino-1-propanol and2-amino-1-butanol did not splatter as much and did not vapor depositcopper. All the complexing agents produced copper films. The bestcomplexing agent appeared to be 3-amino-1-propanol as it formed the mostcontinuous copper films that also showed high conductivity.

Example 35

Example 1 from U.S. Pat. No. 5,378,508 by Castro was repeated usingcopper formate and Duomeen OL (Akzo Nobel, Amersfoort, Netherlands) in awater, acetic acid, and methanol solution to produce a tacky light bluedeposit. Instead of decomposing this deposit with a laser as isdisclosed by Castro, the material was decomposed on a hotplate at 200°C. under nitrogen flow. The resulting deposit showed some signs ofdecomposition to copper but was very discontinuous and contained residuefrom the surfactant.

Example 36

A composition was formulated with 3 wt. % Cu-formate xH₂O (x˜2); 3 wt %nickel formate 2H₂O; 9 wt. % ammonium hydroxide; and 85 wt. % DI water.When decomposed under Nitrogen in TGA gave a Cu—Ni alloy by XRD. Thisshows that complexing agents and combinations of similar metalprecursors work to produce alloys.

Example 37

A 50:50 Cu:Ni precursor composition was prepared using Cu-formate-xH₂O(x˜2) and Ni-formate 2H₂O complexed with 3-amino-1-propanol in DI H₂O.The precursor composition was decomposed under nitrogen cover/flow gasat 350° C. to produce a metallic looking and conductive deposit. Thedeposit had a nickel colored sheen and was very porous. The depositshowed to be a Cu—Ni alloy by XRD. This shows that an alloy deposit canbe produced by conventional processing.

Example 38

A copper precursor composition was formulated containing equal parts byweight of Cu-formate xH₂O (x˜2), 3-amino-1-propanol and water. Thecomposition was deposited on a glass substrate and rapidly heated to350° C. The temperature was held at 350° C. for less than 10 seconds,and then rapidly cooled to room temperature. A Scanning ElectronMicroscope (SEM) photomicrograph showed the film to be dense and x-raydiffraction (XRD) showed that the film contained copper with smallamounts of copper oxide. The film had a resistivity of 40 times the bulkresistivity of pure copper metal. This shows that with fast ramp rates,copper deposits can be produced in air.

Example 39

The same precursor composition as in above example was processed at 300°C. with rapid heating and cooling. The conductivity of the resultingfilm was measured at approximately 3×10⁸ times the bulk copperresistivity while XRD results were identical to Example 33. This showsthat kinetics of decomposition are critical to achieving a conductivedeposit in air.

Example 40

A precursor composition was formulated including 13 wt. % Cu-formate; 16wt. % 3-amino-1-propanol; 58 wt. % deionized water;,and 20 wt. % ethanol(95%). The precursor composition had a surface tension of 31 dynes/cm.and a viscosity of 5 centipoise at a shear rate of 132 Hz. Thecomposition was deposited on ink-jet paper using an ink-jet printer. Theprecursor composition was rapidly heated in air and cooled and resultedin conductive traces. This shows that a modified precursor compositioncan be deposited using an ink-jet to produce conductive traces, in air.

Example 41

A precursor composition including 30 weight percent Cu-formate-xH₂O(x˜2), 40 weight percent 3-amino-1-propanol and 30 weight percent waterwas deposited and processed on glass, FR-4, and Kapton at 200° C. undera nitrogen atmosphere. The resulting films when scraped with a razorblade rolled up, behaving much like a foil. The films were dense and hadan average resistivity of 10 times the resistivity of bulk copper. Thisexample demonstrates that conductive copper features can be formed byprocessing the precursor compositions under an inert gas, such asnitrogen.

Example 42

The above precursor composition was deposited with a quill pen onto FR-4and glass. Conductive traces could be made when lines were processedunder nitrogen at 200° C. In certain thin areas solvent evaporation tookplace before decomposition occurred. In theses cases recrystallizationof the copper formate took place and the film was discontinuous.

Large drops of precursor composition were also deposited and dried. Inone instance a deposit was dried at 90° C. for 40 minutes leading topartial drying and some crystallization. Upon decomposition at 200° C.,however, crystals redissolved and decomposition to copper was complete.When a drop was dried further until no remaining solvent was apparentand crystals changed from dark blue to light blue-green beforeprocessing, the resulting deposit took longer (few minutes) to fullyconvert to copper and resulted in a porous, discontinuous andmechanically weak deposit.

This shows that presence of the complexing agent and solvent isnecessary for proper film formation and conversion to a dense film.Therefore, precursor composition should not be dried before processingand decomposition kinetics need to be fairly rapid in order thatdecomposition takes place faster than drying.

Example 43

The precursor composition of Example 42 was deposited on glass, FR-4,and KAPTON and processed at 180° C. and at 150° C. under nitrogen. Theresulting films averaged 47 times the bulk copper resistivity and 390times the bulk copper resistivity, respectively.

Example 44

A composition was formulated with 27 wt. % Cu formate xH₂O (x˜2); 27 wt.% DI water; 32 wt. % 3-amino-1-propanol; and 14 wt. % dimethyacetamide.Drops were decomposed on glass under nitrogen flow at 200° C. on a hotplate. Bulk resistivity measurements yielded 10× bulk copper on average.The solution was modified with an addition of tetraamine palladiumhydroxide. Samples of both the solution with and without the palladiumprecursor addition were decomposed on a hotplate in air at 200° C. Thesample without the addition did form copper by XRD with indication ofcopper oxides as well, but the deposit was dark with residue and did notappear to be completely decomposed. The sample with the tetraaminepalladium hydroxide addition decomposed in a few seconds to a copperylooking conductive deposit which showed to have no oxide present in ashort XRD scan and no separate Pd peaks. The ratio of Cu to Pd was about2% Pd by weight. This shows that an additional metal precursor may actas a catalyst for decomposition while also forming an alloy.

Electrocatalysts

The following examples illustrate low viscosity compositions for thedeposition of PEM MEA electrodes.

Example 45

1 gram of a 20 wt. % platinum on carbon (Pt/C) electrocatalyst, wherethe carbon support is an acetylene carbon (SHAWINIGAN BLACK, availablefrom Chevron Chemical Company, Houston, Tex.), was dispersed in 2 ml ofde-ionized water and 10 ml of a 5% solution of a sulfonatedperfluorohydrocarbon polymer (NAFION, available from E.I. duPontdeNemours, Wilmington, Del.) to yield final composition after drying ofthe solvent of 67 wt. % catalyst and 33 wt. % NAFION. The compositionwas sonicated in a water bath for at least 10 min. The particle sizedistribution for this composition is a d₁₀ of 1.9 μm, a d₅₀ of 4.7 μmand a d₉₅ of 16.0 μm. The viscosity was measured to be 10 centipoise inthe range of 5 to 50 rpm.

Example 46

1 gram of 60 wt. % Pt/C electrocatalyst, where the carbon support is ahigh surface area carbon (KETJENBLACK, available from Akzo Nobel,Amersfoort, Netherlands), was dispersed in 2 ml of de-ionized water and10 ml of 5 wt. % NAFION solution to yield a final composition afterdrying the solvent of 60 wt. % catalyst and 40 wt. % NAFION. Thecomposition was sonicated in a water bath for at least 10 min. Theparticle size distribution for this composition is a d₁₀ of 3 μm, a d₅₀of 6 μm and a d₉₅ of 14 μm.

The following examples illustrate ink-jettable compositions that areuseful for the fabrication of DMFC (direct methanol fuel cell)electrodes.

Example 47

1 gram of 60 wt. % precious metals (Pt, PtRu) on carbonelectrocatalysts, where the carbon support is KETJENBLACK, was dispersedin 6 grams de-ionized water and NAFION solution (5% by weight) to have afinal weight ratio of 85:15 of dry catalyst to NAFION in the finalelectrode structure. The composition was then mildly sonicated using abath. The particle size distribution for this composition was a d₁₀ of3.4 μm, a d₅₀ of 6.5 μm and a d₉₅ of 16.8 μm. Viscosity was measured tobe 23 centipoise at 5 rpm and 92 centipoise at 50 rpm. The compositionhad a surface tension of 30 mN/m.

Example 48

1 gram of porous, micron-sized pure Pt particles prepared by a sprayconversion method was dispersed in 10 gram de-ionized water bysonication using an ultrasonic horn. A NAFION solution (5% by weight)was then added to have a final weight ratio of 90:10 of dry catalyst toNAFION in the final electrode structure. The viscosity of this ink wasabout 7 to 10 centipoise with a surface tension of 30 mN/m. The particlesize distribution for this ink was a d₁₀ of 1 μm, a d₅₀of 3.2 μm and ad₉₅ of 10.6 μm.

Example 49

1 gram of Pt blacks was dispersed in 10 grams de-ionized water bysonication using an ultrasonic horn. A NAFION solution (5% by weight)was then added to have a final weight ratio of 90:10 of dry catalyst toNAFION in the final electrode structure. The particle size distributionfor this ink was a d₁₀ of 1 μm, a d₅₀ of 5 μm and a d₉₅ of 20 μm.

Example 50

As is discussed above, preferred precursors for platinum metal accordingto the present invention include chloroplatinic acid (H₂PtCl₆.xH₂O),tetraamineplatinum (II) nitrate (Pt(NH₃)₄(NO₃)₂), tetraamineplatinum(II) hydroxide (Pt(NH₃)₄(OH)₂), tetraamineplatinum (II) bis(bicarbonate)(Pt(NH₃)₄(HCO₃)₂), platinum nitrate (Pt(NO₃)₂), hexa-hydroxyplatinicacid (H₂Pt(OH)₆), platinum (II) 2,4-pentanedionate (Pt(acac)₂), andplatinum (II) 1,1,1,5,5,5-hexafluoro 2,4-pentanedionate (Pt(hfac)₂).Other platinum precursors include Pt-nitrates, Pt-amine nitrates,Pt-hydroxides, Pt-carboxylates, Na₂PtCl₄, and the like.

The Pt precursor is dissolved in either water or organic based solventup to 30 wt. % concentration. A portion of appropriate solvent (water ororganic based) is slowly added to a carbon dispersion similar to GRAFO1300 (Fuchs Lubricant, Harvey, Ill.), while being shear mixed to achieveup to 30 wt. % solids loading dispersion. A solution of Pt precursor isthen slowly added to the shearing carbon dispersion. The resultingcomposition is then shear mixed for an additional 10 minutes. Theviscosity for a 5 wt. % solids loading dispersion was measured to be 3to 4 centipoise with surface tension of 77 mN/m.

Example 51

A TEFLON coated KAPTON substrate was selectively coated with a removableprotective coating exposing a 100 μm wide trench of the underlyingTEFLON coating. This substrate was dipped into an etchant (TETRA-ETCH,available from W.L. Gore and Associates) that forms a hydrophilicsurface, followed by a rinse in water and removal of the adhesiveprotective coating. This resulted in a hydrophobic surface (naturalsurface of TEFLON) with a 100 μm wide hydrophilic strip from theetchant. The substrate was subsequently drop coated with a silverprecursor composition containing 33 grams Ag-trifluoroacetate, 33 gramsH₂O, 33 grams DEGBE and 1 gram lactic acid. The composition was observedto be confined to the hydrophilic surface strip. After heating of theconfined composition to 200° C. for 5 minutes, a 100 μm wide silver linewas obtained with a bulk resistivity of about 3 times the bulkresistivity of pure solid silver.

This example demonstrates the ability to confine a low viscosityprecursor composition through surface modification of the substrate.

Example 52

A precursor composition was formulated by combining 0.24 grams palladiumtrifluoroacetate, 7.3 grams silver trifluoroacetate, 37.5 grams silverflake, 5.13 grams terpineol, 1.55 grams N-methyl-pyrolidone. Thismixture was fired at 185° C. for 60 minutes to yield a resistivity of2.3 times the bulk resistivity of pure silver.

Example 53

A precursor composition was formulated by combining 35 grams silverflake, 7.55 grams silver (I) oxide and 5.35 grams terpineol. Thismixture was fired at 185° C. for 60 minutes to yield a resistivity of2.4 times the bulk resistivity of pure silver.

Example 54

A precursor composition was formulated by combining 35.03 grams silverflake, 6.26 grams silver nitrite, 6.51 grams terpineol. This mixture wasfired at 185° C. for 60 minutes to yield a resistivity of 2.1 times thebulk resistivity of pure silver.

Example 55

A precursor composition was formulated including 16.5 grams metallicsilver powder, 3.5 grams alpha-terpineol and 5 grams silver carbonate.This composition was deposited and heated to 350° C. The resultingconductive trace had a resistivity of 29 times the bulk resistivity ofpure silver.

Example 56

A precursor composition was formulated including 10 grams silver oxide,0.9 grams silver nitrate, 20 grams metallic silver powder, 2.1 gramsDMAc and 5.0 grams terpineol. The composition was deposited and heatedto 350° C. The resulting conductive trace had a resistivity of about 11times the,bulk resistivity of silver.

Examples of In-Situ Precursor Generation

Example 57

Comparative Example

Silver oxide (AgO) powder was tested using TGA at a constant heatingrate of 10° C./min. The TGA showed the conversion to pure silver wascomplete by about 460° C.

Example 58

A mixture of 3.2 grams silver oxide and 3.0 grams neodecanoic acid wasanalyzed in a TGA. The analysis demonstrated that the conversion to puresilver was substantially complete by about 250° C.

Example 59

A mixture of 5.2 grams alpha terpineol, 4.9 grams silver oxide and 1.1grams neodecanoic acid was analyzed in a TGA. The TGA demonstrated thatthe conversion to pure silver was substantially complete by about 220°C.

Example 60

The silver oxide/carboxylic acid chemistry was modified by the additionof metallic silver powder. The reaction products from the silver oxideand carboxylic acid weld the silver particles together providing highlyconductive silver traces and features.

Example 61

A precursor composition was formulated that included 102.9 grams silvermetal powder, 7.8 grams silver oxide, 15.2 grams silver nitrate, 10.1grams terpineol and 1.5 grams, SOLSPERSE 21000. The precursorcomposition was deposited and was heated to 250° C. The resultingconductive features had a resistivity that was less than 6 times thebulk resistivity of pure silver. The material was very dense and had lowporosity. This mixture was analyzed in a TGA and showed a conversion tosilver at about 270° C.

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe spirit and scope of the present invention.

1. A process for forming a solar cell conductive feature, comprising:(a) direct printing a precursor composition onto a substrate, theprecursor composition comprising at least one of metallic particlescomprising a metal or a metal precursor compound to the metal; and (b)heating the composition to a temperature not greater than 300° C. toform the solar cell conductive feature on the substrate, wherein theconductivity of the solar cell conductive feature is no less than 10percent the conductivity of the equivalent pure metal.
 2. The process ofclaim 1, wherein the direct printing comprises syringe printing.
 3. Theprocess of claim 1, wherein the direct printing comprises aerosol jetdeposition.
 4. The process of claim 1, wherein the direct printingcomprises ink jet printing.
 5. The process of claim 4, whereint thetemperature is not greater than 250° C.
 6. The process of claim 4,wherein the temperature is not greater than 185° C.
 7. The process ofclaim 4, wherein the substrate comprises a polymer.
 8. The process ofclaim 4, wherein the substrate has a softening point of not greater than225° C.
 9. The process of claim 1, wherein the conductive feature has aresistivity that is not greater than 4 times the resistivity of theequivalent pure metal.
 10. The process of claim 1, wherein theconductive feature has a resistivity that is not greater than 2 timesthe resistivity of the equivalent pure metal.
 11. The process of claim1, wherein the precursor composition comprises the metallic particles,and wherein the heating sinters adjacent metallic particles to oneanother.
 12. The process of claim 11, wherein the metal is selected fromthe group consisting of silver, palladium, copper, gold, platinum andnickel.
 13. The process of claim 1, wherein the precursor compositioncomprises the metal precursor compound.
 14. The process of claim 13,wherein the metal is selected from the group consisting of silver,palladium, copper, gold, platinum and nickel.
 15. The process of claim1, wherein the conductive feature comprises a set of finger lines andcollector lines deposited essentially at a right angle to the fingerlines.
 16. The process of claim 15, wherein either or both the parallelfinger lines or the collector lines have width less than 200 μm.
 17. Theprocess of claim 15, wherein either or both the parallel finger lines orthe collector lines have width less than 100 μm.
 18. The process ofclaim 1, wherein the conductive feature has a thickness greater than 5μm.
 19. The process of claim 1, wherein the conductive feature comprisesa transparent conductive feature.
 20. The process of claim 1, whereinthe conductive feature comprises indium-tin oxide or antimony-tin oxide.21. The process of claim 1, wherein the precursor composition comprisesthe metallic particles, the metallic particles having a volume medianparticle size of not greater than 100 nanometers.
 22. The process ofclaim 1, wherein the precursor composition comprises the metallicparticles, the metallic particles having a volume median particle sizeof not greater than 0.3 μm.
 23. The process of claim 22, wherein themetallic particles comprise a cap or coating thereon.
 24. The process ofclaim 23, wherein the cap or coating comprises an inorganic cap orcoating.
 25. The process of claim 23, wherein the cap or coatingcomprises silica.
 26. The process of claim 23, wherein the cap orcoating comprises an organic cap or coating.
 27. The process of claim23, wherein the cap or coating comprises a polymer.
 28. The process ofclaim 23, wherein the cap or coating comprises an intrinsicallyconductive polymer, a sulfonated perfluorohydrocarbon polymer,polystyrene, polystyrene/methacrylate, sodium bis(2-ethylhexyl)sulfosuccinate, tetra-n-octyl-ammonium bromide or an alkane thiolate.29. The process of claim 23, wherein the cap or coating comprises PVP.30. The process of claim 1, wherein the conductive feature is resistantto solder leaching.
 31. The process of claim 1, wherein the processfurther comprises surface modifying the substrate with a laser.
 32. Aprocess for forming a solar cell conductive feature, the processcomprising heating an ink jet printed precursor composition comprising ametal to a temperature not greater than 300° C. to form the solar cellconductive feature on a substrate, wherein the conductivity of the solarcell conductive feature is no less than 10 percent the conductivity ofthe equivalent pure metal.
 33. The process of claim 32, wherein theprecursor composition comprises at least one of metallic particlescomprising the metal or a metal precursor compound to the metal.
 34. Theprocess of claim 33, wherein the temperature is not greater than 250° C.35. The process of claim 33, wherein the temperature is not greater than185° C.
 36. The process of claim 33, wherein the substrate comprises apolymer.
 37. The process of claim 33, wherein the substrate has asoftening point of not greater than 225° C.
 38. The process of claim 33,wherein the conductive feature has a resistivity that is not greaterthan 4 times the resistivity of the equivalent pure metal.
 39. Theprocess of claim 33, wherein the conductive feature has a resistivitythat is not greater than 2 times the resistivity of the equivalent puremetal.
 40. The process of claim 33, wherein the precursor compositioncomprises the metallic particles, and wherein the heating sintersadjacent metallic particles to one another.
 41. The process of claim 40,wherein the metal is selected from the group consisting of silver,palladium, copper, gold, platinum and nickel.
 42. The process of claim33, wherein the precursor composition comprises the metal precursorcompound.
 43. The process of claim 42, wherein the metal is selectedfrom the group consisting of silver, palladium, copper, gold, platinumand nickel.
 44. The process of claim 33, wherein the conductive featurecomprises a set of finger lines and collector lines depositedessentially at a right angle to the finger lines.
 45. The process ofclaim 44, wherein either or both the parallel finger lines or thecollector lines have width less than 200 μm.
 46. The process of claim44, wherein either or both the parallel finger lines or the collectorlines have width less than 100 μm.
 47. The process of claim 33, whereinthe conductive feature has a thickness greater than 5 μm.
 48. Theprocess of claim 33, wherein the conductive feature comprises atransparent conductive feature.
 49. The process of claim 33, wherein theconductive feature comprises indium-tin oxide or antimony-tin oxide. 50.The process of claim 33, wherein the precursor composition comprisesmetallic particles, the metallic particles having a volume medianparticle size of not greater than 100 nanometers.
 51. The process ofclaim 33, wherein the precursor composition comprises metallicparticles, the metallic particles having a volume median particle sizeof not greater than 0.3 μm.
 52. The process of claim 51, wherein themetallic particles comprise a cap or coating thereon.
 53. The process ofclaim 52, wherein the cap or coating comprises an inorganic cap orcoating.
 54. The process of claim 52, wherein the cap or coatingcomprises silica.
 55. The process of claim 52, wherein the cap orcoating comprises an organic cap or coating.
 56. The process of claim52, wherein the cap or coating comprises a polymer.
 57. The process ofclaim 52, wherein the cap or coating comprises an intrinsicallyconductive polymer, a sulfonated perfluorohydrocarbon polymer,polystyrene, polystyrene/methacrylate, sodium bis(2-ethylhexyl)sulfosuccinate, tetra-n-octyl-ammonium bromide or an alkane thiolate.58. The process of claim 52, wherein the cap or coating comprises PVP.59. The process of claim 33, wherein the conductive feature is resistantto solder leaching.
 60. The process of claim 33, wherein the processfurther comprises surface modifying the substrate with a laser.